well 
for one

the main thing that makes the USD different is that it is the *most saleable good*. accepted practically anywhere.

that is another of the primary characteristics that makes it "money"
and bottles of water are not because they are only salable based in their utility

that is why prices are *accounted* in USD. and not something else.

so
while i see your point
it doesn't really express the reality of the situation

people *account* in USD *units* because it is universally saleable.

that is just how the world is
not saying it *should* be this way
but its a fact. 

 To elaborate on this point I would like to refer the reader to Ludwig von Mises "Theory of Money and Credit"
pg 48, Money as a Price Index

"Nowadays exchange is usually carried on by means of money, and since every
commodity has therefore a price expressible in money, the exchange-
value of every commodity can be expressed in terms of money. This
possibility enabled money to become a medium for expressing values when the growing elaboration of the scale of values which resulted from the development of exchange necessitated a revision of the technique of valuation.
That is to say, opportunities for exchanging induce the individual
to rearrange his scales of values. A person in whose scale of values the
commodity 'a cask of wine' comes after the commodity 'a sack of oats' will reverse their order if he can exchange a cask of wine in the market for a commodity that he values more highly than a sack of oats. The position of commodities in the value-scales of individuals is no longer determined solely by their own subjective
use-value, but also by the subjective use-value of the commodities that can be obtained in exchange for them, whenever the latter stand higher than the former in the estimation of the individual. Therefore, if he is to obtain the maximum utility from his resources, the individual must familiarize himself with all the prices in the market.
For this, however, he needs some help in finding his way among the confusing multiplicity of the exchange-ratios. Money, the common medium of exchange, which can be exchanged for every commodity
and with which every commodity can be procured, is pre-eminently suitable for this. It would be absolutely impossible for the individual, even if he were a complete expert in commercial matters, to follow
every change of market conditions and make the corresponding alterations in his scale of use- and exchange-values, unless he chose some common denominator to which he could reduce each exchange-
ratio. Because the market enables any commodity to be turned into money and money into any commodity, objective exchange-value is expressed in terms of money. Thus money becomes a price-
index, in Menger's phrase." 

 To elaborate on this point I would like to refer the reader to Ludwig von Mises "Theory of Money and Credit"
pg 48, Money as a Price Index

"Nowadays exchange is usually carried on by means of money, and since every
commodity has therefore a price expressible in money, the exchange-
value of every commodity can be expressed in terms of money. This
possibility enabled money to become a medium for expressing values when the growing elaboration of the scale of values which resulted from the development of exchange necessitated a revision of the technique of valuation.
That is to say, opportunities for exchanging induce the individual
to rearrange his scales of values. A person in whose scale of values the
commodity 'a cask of wine' comes after the commodity 'a sack of oats' will reverse their order if he can exchange a cask of wine in the market for a commodity that he values more highly than a sack of oats. The position of commodities in the value-scales of individuals is no longer determined solely by their own subjective
use-value, but also by the subjective use-value of the commodities that can be obtained in exchange for them, whenever the latter stand higher than the former in the estimation of the individual. Therefore, if he is to obtain the maximum utility from his resources, the individual must familiarize himself with all the prices in the market.
For this, however, he needs some help in finding his way among the confusing multiplicity of the exchange-ratios. Money, the common medium of exchange, which can be exchanged for every commodity
and with which every commodity can be procured, is pre-eminently suitable for this. It would be absolutely impossible for the individual, even if he were a complete expert in commercial matters, to follow
every change of market conditions and make the corresponding alterations in his scale of use- and exchange-values, unless he chose some common denominator to which he could reduce each exchange-
ratio. Because the market enables any commodity to be turned into money and money into any commodity, objective exchange-value is expressed in terms of money. Thus money becomes a price-
index, in Menger's phrase." 

 I'll just stick with I don't get it and don't understand and wouldn't get the explanation if someone took the time to give me one and skip the holier than thou cuntchutery boards.  

 doesn't seem like it should be THAT hard to understand.
its like "the fish doesn't see the water"

and some people dont care to think about it. 

 Drowning in usd with no one to exchange the unit with because they didn't account sort of fish.