Revision said:
Um, game caps at 56k so it doesn't matter what speed you have beyond that guys.
What matter is latency, and having DSL/Cable or FTTx line helps to reduce latency. Nobody cares about amount of bytes exchanged between you and the server, beside SE. Most of MMO out there barely download more than couple of KB/s in any given situation.
You gotta think about something : The more data your client download, the more data SE servers upload. That's why MMOs network code is optimized so your client doesn't suck bandwidth of the game service provider.
SE don't give a f**k about 56k users, however they care about their servers/wallet. The less data they send to you, the less $ you cost. Now in 2009 it's not a big deal, especially for a corporation like SE. Back in 2003 however :/