its rather simple. if they quote you the rate in teh Local currency then when you go to pay they are Stuck with the amount in Loacl Currency. Now if they qoute it to you in US$ or whatever, then upon check-out is when they will figure out how much it comes to in local currency.
In countries where there is usually devaluations or where the Local currency has a trend to go down against the US$ they are basically Hedging themselves. Happened to me recently in Guatemala where it was 7.4 when I got there and 7.8 a few days later when I left. I also couldnt pay it in US$ I could have in the Local Currency but at the rate of 7.8 per $1.
Then of cause the CC adds their % so its basically a rip-off. most of teh World does it this way. could be if Marriot has alocal web-site you might beable to book it in teh Local currency but I doubt they will take US$ from you to settle the bill.