I'm not exactly sure if you're saying this - that at some point all the other manufacturers will drown out Apple's iPad, because there are so many against one? That might make simple sense, but if we look at the iPad in the same light as the iPod, it makes more sense to think that Apple will simply dominate the market, regardless of the volume of manufacturers trying to compete.
What's more extraordinary is that Apple didn't create the music player, in the same way they created the iPad. What they did with the iPod is create both the consumption device and the ecosystem to feed the consumption. The iPad is just another consumption device (albeit new and revolutionary) that taps into the ecosystem they already have.
They're doing the same thing with Apple TV and if they go forward with an Apple Television, they're again just allowing people to feed off of the ecosystem they created long ago. It's a brilliant business model and one that is going to be difficult to crack for other manufacturers. Google is trying - but they're trying lots of things, which means they're not so singularly focused like Apple. Same thing with Amazon, although they really are just a store that sells everything and if you've ever been on the selling side, you'll know that having an almost unlimited number of choices for products to sell can be more of a hindrance than a help.