Their specs are very, very close to each other. The iPhone has twice the L1 cache (32+32 to the droids 32) but I don't see that making a huge difference, both have 256megs of ram, CPU clocked at 600 (droid is actually 550 but its not enough to make a huge difference). The only thing I see making a huge difference is the droid's higher resolution at 854x480 versus the iPhone 3GS' lesser resolution at 480x320. Higher definition, higher demand perhaps. Could also be a bug in the Droid's OS. Could be both.
I, personally, LOVED the droid.. when it was new. I agree though that it has been some what lack-luster after all these... 2 years. Root and overclock helps a lot though. If your phone can handle it that is.