Melonite may be the same as Tennifer, but it must be that Glock has come close to perfecting the process and S&W has not. I say "come close" since we have a G17 slide at work with rust on it, with no damage, that we are sending back to Glock to be refinished. It's a Gen 3 that's about 7 years old.
OTOH, another one of our locations switched to 9mm M&P's, and they are having a lot of slide rusting problems.