As a consumer it is annoying because we have to lock in some universal-to-us currency (US dollars) for various specific currency (MS Points, Amazon Coins, etcetera).
I assume the larger organizations make some significant money on a large number of small 'points' that never get redeemed, in addition to having the actual cash for investment or arbitrage.
Hmm, reminds me I have some MS Points I should spend. And some PSN currency too. And soon some Amazon Coins...