First off: Danskmacabre outed as a family man! Gosh!
Re: Mike's original point, it's an interesting idea that I admit I've never considered -- that your handheld could be a sort of hub that could output onto different nearby screens such as TVs if available. Certainly the leap from PS1 to PS2 was the critical one in terms of generally acceptable fidelity. PSP 2 should manage PS2+ graphics, so the ability to have a portable that you play on the move and then play on your TV is certainly there.
Two points. Firstly, if a designer makes a game assuming it's always going to be played on a handheld, he or she will make certain compromises that they won't make if they know it will be on a telly. And vice-versa (in reverse). In other words, the experience is likely to be compromised in some way?
Second up, handhelds will really have to address the control issue if they're to be a main point of play. Even the DS isn't perfect; sure the stylus is fab, but I'd like to see you control a TV-based Metroid using it on a handheld. Control is 50% of games; vision and sound are the other 50% (and yes, the fabled 50% each split between them). But because you are the character, control is all. Handhelds aren't competing at the highest level yet.