You misunderstood me in a few places, and not all of my comments were directed specifically at you.
Mahlikus posted a link to the UV mapping page of the Zbrush wiki which talks primarily about textures and UV tiles. A lot of folks don’t fully understand what PTex is, so it often gets confused with the tiling in Zbrush which isn’t really the same. With Ptex, each polygon gets its own texture map, of which each can have its own resolution that can be changed at any time. All the resulting texture maps are stored in a single .ptx file. PTex also does some nifty filtering which prevents seams from becoming visible. The way Zbrush does tiling is to break each polygon into a rectangular shaped traditional UV, with all of the individual UV rectangles fitting on one single texture. It is possible to run out of resolution this way, and it doesn’t render very well outside of Zbrush (especially displacements).
Regarding game engines, I was talking about the needs of artists who work outside of Zbrush versus those who don’t. I know that PTex isn’t really suited for real-time rendering, at least until graphics technology improves. Zbrush is being used in 3D workflows everywhere these days (cinema & television, video game assets, printing, etc), and not just as a simple illustration tool. This is why we’ve seen so many export-centric additions since ZB 2.0. As I said before, if you’re not straying outside of Zbrush, polypainting is all you should ever need. For those who use it as part of a larger workflow, UV’s are an important aspect regardless of type, outdated or not. The idea behind PTex is to do away with traditional UV’s and all their inherit problems. And yes, it works with non-quad geometry too (with subdivision).
Polypainting is basically vertex painting, is it not? Zbrush is already doing some behind the scenes calculations/tracking to make sure all that paint stays where it’s meant to, which is especially important when making mesh modifications. The same thing can be done for Ptex as well. The only limitation is the amount of coding work the developer is willing to do. There is really no reason why an artist cannot make major modifications without screwing up their various paint layers when using Ptex (normal, specularity, diffuse, reflection, and so on). At least that is the impression I got from what I’ve read thus far. I have no idea how big of an undertaking this would be for Pixologic, but the competition doesn’t seem to be having too much difficulty. PTex, which is open source, is still under development as far as I can tell, meaning it should continue to improve as time passes.
This page has some interesting information posted by someone at Pixar. I should point out that the “can’t paint them flat” comment they made isn’t 100% accurate. I recently watched a video showing Mudbox passing Ptex texturing off to Photoshop and then back again, very similar to what ZAppLink does. Not technically flat, but close enough and better than nothing. You can find more interesting info on this page as well, which talks a little bit about its goal and capabilities. Finally, there is this site where you can talk with Disney employee Brent Burley, the developer of Ptex. Some of the other comments (mostly by other developers) are worth a read too.
In all honesty, polypainting and Ptex are two sides of the same coin. Whereas polypainting works best with high poly meshes, Ptex works best with low to mid density meshes (though from what I’ve read, million poly meshes might be workable too). As I said before, we’ll see Ptex support in all the major 3D apps long before we see something akin to the polypainting Zbrush does. When it becomes feasible to animate and render multiple million poly meshes in programs like Maya and 3ds Max, then we’ll probably see vertex painting take off. For now it is only useful to Zbrush. Unless you’re baking textures of course, in which case mapping of some sort will still be required, bringing us back to square one. Semi-automatic unwrapping algorithms (i.e. UV Master et al) are great, but all are still far from perfect. PTex solves all of that very simply, plus it truly is a huge time saver. Endless hours of tweaking UV’s can now be spent creating art and producing assets. Who won’t be grateful for that? 
Longest…wait…ever!