For you and those who have this problem understanding the "K and M system": wikipedia - metric prefix. For example: a "99k" means 99 000 mainly. But this has the range from 98 500 to 99 499 (and not 9 999, which would be 10k).
The reason behind the item squish is not founded in the ignorance and personal preference of the players but in technical limitations of the WoW engine (and therefore the computers limitation). They already went to a system in MoP for a better readability with ' and other delimiters. And as several other people said: you can choose your own cosmetic addon to "lower" the numbers from "324 638" to "325k" (which is pretty nice I'd like to add).