One of the biggest selling points for PlayStation Portable was, according to Sony, the ability to play console-quality games on-the-go. In essence, having a PSP was like taking your PS2 with you - more gaming goodness, more connectivity, and most of the hardware necessary to deliver graphics on par with the PS2.
Unfortunately, PSP history shows an alarming number of rushed ports. Third-party developers leveraged the PSP's power with unique experiences less and dumped slightly-worse versions of console games on it more. It's a notable low point in the PSP's lifecycle, so it's strange that Sony has more-or-less adopted the same strategy for marketing PlayStation Vita - it's a console-quality piece of hardware that you can take anywhere.