Every market I've seen lists "prices" in BTC. I know we are paying in BTC but it's way easier to compare prices on things and calculate totals with shipping etc if the prices were in USD (or whatever your selected currency was). The sites already show the live exchange rate, and I'm sure when vendors list products they list what USD price they want and it converts to Bitcoin on the fly. Why not just keep the prices shown in USD and the only conversion the site needs to do is show what your current Bitcoin balance is worth? It'd be way easier.
lol I'm pretty sure like every single DNM has the option to change it.