I wondered the same thing. I connected via Wi-Fi to my Verizon FiOS router, which has symmetric internet connectivity at 25Mb/s both up and down. Using the default settings on the Droid, I see the SpeedTest needle pinned at a solid 10Mb/s down, but only get 1MB/s up. That would seem to jibe with the default '05 Data Rates' settings. But even after changing them to 153.6/153.6, I saw identical results although I'd expected to see 10Mb/s in each direction.
I also tried 3G connectivity with both settings. My home is in a very weak signal area for VZW Wireless, so I have yet to see EVDO speed test numbers here showing much more than about 300-400k down (I get about 4x those speeds in other parts of town that are closer to towers). But after making the change to 153.6/153.6, I am suddenly seeing 800-900k down very consistently.
Neither result makes any sense to me: Why would I not see equal speeds up/down via my wi-fi link after making the change? And why would a change to the upload speed limit cause the download speeds of a 3G connection to improve? All very strange. Anyway, I'm going to leave the setting at 153.6/153.6 for awhile just to see what happens in actual usage, and to see if I continue to experience the higher download speeds in a weak-signal area.
Has anyone else tried changing this setting?