Most services do cover water damage, so that's weird. Most protection plans that I'm aware of are basically just... send us $50, get the same phone again whenever. I guess T-Mobile has changed since I used them. I'm on my 4th phone of the same model with Sprint, so yeah, I pretty much think if you don't have a protection plan, you're an idiot. It isn't that I treat my phone badly, I actually take pretty good care of it, but mishaps are bound to happen when you carry something with you virtually everywhere. I lost one in a hot tub, one because I threw it against a wall in a fit of rage (whoops), and another because the battery stopped fitting properly and it would just shut off all the time.
If you're using a device that costs that much money and you're going to be using it often enough for the chance of breakage or loss to be that high, it only makes sense to protect the investment.