I'm assuming that by XT9 you mean the predictive spell correction, right? Anyway, here's the deal:
The Android keyboard is context sensitive. There's the default mode for entering text, that's when you see the predictions pop up left and right. But the keyboard knows when you're typing in a search bar, or an address field, that's why it can show you the @ and .com keys. Also it seems, prediction is suppressed for these modes. You can turn prediction on and off in the keyboard settings menu, but it won't affect these modes. I can understand how this might not be useful for a search bar, special but uncommon words would get corrected all the time even though you want to enter those specific words, and a URL bar is a completely different matter... Still, if you want prediction in these fields you'll have to go 3rd party keyboard I guess, Swype can do it's thing anywhere for example.