Orion is the future manned NASA vehilce. Because of the fact that NASA won't use any different system to carry humans up into space, Orion will be the replacement of the Space Shuttle indeed, not as a reusable glider, but as a spacecraft.
A lot of people at present are to narrow minded in my point of view (too much fanatic on old stuff) -> focused on the ISS and Hubble, two aging relicts, to try to justify further use of the Space Shuttle. Hubble is in its declining years. Follow up space telescopes won't require a Space Shuttle, nor are they launched by such a vehicle. As for the ISS: this thing also is aging. It's already 10 years old and in the worst case it might not get beyong 2016. And Remember that the Russians did not need a Space Shuttle to build and operate the Mir space station. I hope that NASA won't be that s****d again to carry up such a big space station like the ISS by such small/light pieces.
As for the gap:
The Space Shuttle has caused a gap way bigger than Constellation does right now and is indicating to do in near future. If you add the gaps of the Shuttle program, it's already nearly a decade. Yes, a decade. The delays during development already were so "amazing" (because of major problems with the thermal protection system but also main engines and other parts) that it even caused Skylab to be abandoned.
There is only one rational reason to continue using the Space Shuttle: jobs. And I can understand those, nearly 8000 people, who are going to lose their jobs. But NASA has a news focus, which is the deep space again, well, luckily. For that the Shuttle is absolutely useless. That NASA has just announced the STS-134 crew, shows how serious they are regarding the Shuttle retirement and doing something different. Just look how they hurry up now. They try to finish the ISS monster project on time to start doing something different.
NASA is on a good path, no matter they chose Ares or something else.
