I agree with jen9159, if they are good enough friends to invite to the shower, they should be on your "A" list for your wedding anyways. Your "B" list should be the people you would like to have come, but if they can't it would be okay.

As far as inviting people to the wedding and not the reception, I had a friend who invited a lot of people to the wedding and to only the dance part of the reception, not the dinner part. They couldn't afford to feed everyone they wanted there, I don't know if it's something I'd do, but it's just a suggestion.