Buy.com might be a great generic but it is just that and the company may not own it in all the markets in which it wants to operate.
A trademarked brand is far easier to market.
Depends. Rakatmatakat might be a good brand name in Japan but it sounds less good in the USA, and probably sounds as bad in European tongues as well. Nova was a good brand in the USA but meant "Doesn't Run" in Spanish. A trademarked brand isn't necessarily easier to market, which is why some brands have different names across borders, like Exxon and Esso. Esso is easier to pronounce in Spanish than the less sensible Exxon.
Consolidating brand names globally, particularly a name like Ratakakatat, might not be a good solution.