To take your diligence one step further, I have come up with a few similar comparisons (I don't have Echoes - yet ) using The Wall tracks 4 and 5, and captured the line in playback in Sound Forge in an effort to quantify the results. I am using 2b7 and Hijack v80.

Here's a screenshot of a side-by-side comparison of the transitions. I did not even think about trying straight wav's earlier until you mentioned it - I've got to stop thinking of it as an 'only' an MP3 player...

Here are the captured results if anyone is interested (zipped wav's, ~530k each)...
4-5wav.zip is just straight wav files. Absoultely zero gap - perfect!
4-5-b128.zip is encoded using just 128k CBR. It has a very noticeable 57 mS gap.
4-5-b128--nogap.zip is encoded with --nogap and 128k CBR. Only a 5 mS gap (barely perceptible).
4-5--r3mix.zip is encoded using --r3mix preset (high Q VBR). 31 mS gap.
4-5--r3mix--nogap.zip is encoded using --r3mix preset (high Q VBR) and --nogap. 5mS gap.
4-5--r3mix-t--nogap.zip is encoded using --r3mix preset (high Q VBR), --nogap, and no Lame VBR header. 5mS gap.

There did not seem to any discernable difference by removing the Lame VBR header. Maybe due to different source material? The gaps are apparently resulting only from the start of the second song. I tried Tony's Gapkiller to trim a few frames, but it seemed to make it worse. Anyone know a way to remove the 5 mS silence at the start of a track, or is this strictly a limitation of the mp3 format?