The redbook format (audio CD) is 44.1 khz, 16 bits. In other words:
44100 hz * 16 bits * 2 channels = 1411200 bps = 1411.2 kbps = ~1411 kbps.
So if you have a redbook format track, it is necessarily 1411 kbps.
MP3 is a lossy compression method and it loses bits, but in a really smart way. Even so, the bits are indeed lost forever. When you convert the MP3 to a CD track, the redbook format requires 1411 kbps, so that's what's written out. But the lost bits are still lost, you just happen to have a 1411 kbps version of the lossy track. It isn't as good as the original though no matter how many kbps winamp tells you it is.
It's sort of like a copier versus a fax machine. Suppose I print something out and then I feed it through the copier. I look at the copy and the original and I see that wow, they're pretty close. Now suppose I take the copy and I fax it to someone else. They take that facsimile and they copy it using a really good photocopier, a better copier than mine actually. The photocopy of the fax, no matter how good that photocopier is will never look as good as the original or the photocopy I took of the original.
