Crappy USB power supplies are, indeed, ubiquitous. That's partly why powering such a high current, voltage-sensitive device like the R-Pi that way is such a lousy idea. Higher voltage, moderate current "wall warts" are even *more* ubiquitous, and regulating their output with a buck converter means that having a less-than-perfect one is much less of a problem.
Also, microUSB connectors can only be inserted in one orientation and the cables are much thicker than necessary for just supplying DC power. That increases the stress on the SMD connector. It's just not the best solution.
The B+ has switching converters for the 1.8 and 3.3 volt power rails, but it still requires 5V power - meaning the problem Pi Power aims to solve is still there.
Pi Power works extremely well with the B+. In fact, one problem with the B+ is that 26 pin IDC (ribbon) cables can't be plugged into the GPIO interface because pins 27 and 28 get in the way. Pi Power - in addition to powering everything - can be used as an adapter to make those cables fit. If you want to use all 40 pins of the GPIO interface, you can use a 14 pin stacking header next to Pi Power.
I don't think Pi Power is overpriced. A proper, high quality 2A USB power supply and a decent cable can cost as much as Pi Power and a surplus 800 mA @ 9V supply.