They look better, cost less, and are holding up pretty well to the test of time in terms of both build quality and usability, to name a few reasons.
Personally, I like the older versions of OS X they run, I like the community built around them, I like using older/outdated things and finding new uses for them, and/or taking on a challenge to help them retain their old uses.
PowerPC Macs are unique and full of character. 🙂
As far as the "once device" solution; perhaps it's just me, but when it comes to electronics, I don't like "do everything" devices. For one, you usually end up compromising on at least one if not more of the multiple functions to achieve having them all. Most people seem to use a smartphone for their music device, alarm clock, and game player. Personally, I'd rather have a phone, an iPod, and a dedicated handheld games device instead; they each perform their respective tasks better than the smartphone ever could, and don't interfere with each other's operation whatsoever.