So the logic of more patches = better profiles is sound in theory. There are however a couple things to consider. Firstly 3rd party profiling software needs to be able to generate profiles for any device, be it a 6 color offset press, a large gamut inkjet printer, or a toner based copier. To accommodate different devices the internal engine needs to be adaptable, and so therefore having more sample points can sometimes offer a noticeable improvement in the profiles, especially with CMYK profiles. With the HP color center the engine knows more or less what the gamut of the printer is. The result is that the color profiling engine has been optimized around the Z31/3200 characteristics, allowing it to produce very good results from fewer patches.
Even when thousands of points are sampled the software may not make equal use of all of the additional data, and virtually all software "smooths" the resulting measurements. There is usually a trade off between accuracy and smoothness of a profile, with photographic output generally favoring the later. What goes on behind the scenes is usually more important than simply the number of profiles being feed to the software.
The APS adds the ability to produce CMYK profiles, useful if your using the printer in conjunction with a RIP or if your going to use your Z series to build profiles for other printers you own. IT also provides basic profile editing tools, and a monitor calibrator, giving you a complete color management package. I've done the tests and I'm generally happy with the results from the color center, but if you need more versatility the APS may be of interest.