No, no, no. None of those encoders add ANYTHING to the file, except an ID3 tag.
The silence at the end of an MP3 lasts less than 20 milliseconds and is inherent in the MP3 format. It's not caused by the encoder, it's caused by the format because MP3 uses fixed-sized frames, so if your song isn't an exact multiple of 20 milliseconds, you'll get less-than-or-equal-to 19.999999 milliseconds of silence at the end.
The way I see it, an audiophile would rightfully be concerned about the very audible, 20 millisecond gap between songs -- but then again, why would an audiophile be using the MP3 format?
I'm not trying to start a war or anything, but it's kinda like complaining about paint chipping off of the hood of my rusted, old Pinto that barely runs anyway -- kind of pointless, given the big picture. If you want true, gapless playback, then there are ways to accomplish that with MP3s. No, you can't just rip a bunch of MP3s separately and expect the software to string them together flawlessly, but you can rip them specifically for a no-gap playback and have them work that way surprisingly well.
MP3 ain't an audiophile, professional, true-to-the-original format, and as such, comes with certain limitations that most casual users will never even know exist.
My question is this: if you use Apple's Lossless format, does it have the same problem? Does AAC also have fixed-size frames? Does it affect other formats other than MP3?