when re-painting a frame, is necessary to strip the frame all the way down to bare metal? can i get a good paint job if i just and it well and use primer that "fills in" and wet-sand? fast eddie outty

Just like a car, you don't "have" to.
1. Make sure you don't have a paint compatibility issue - don't put lacquer over an enamel.
2. If you change the frame's color, any chips and wear wil be multi-colored, and this includes your drop outs, seat binder bolt, water cage bolts, as well as road scars.
And you will have more paint thickness:
3. If you have a lugged frame you will notice the lugs/tube interface fills in a bit.
4. Your clamp on bits, if you have any, may fit just a little differently.
All that being said, I've done it (same color) and am happy with the results.

You don't have to, but I'd recommend at the very least doing a thorough sanding job first to level out any existing scratches, paint chips, etc and to give the primer a good surface to mate to. Yes, primer, more important than anything, use primer and wetsanding to even out the surface and give your color the best possible surface to adhere to.