Usually, a stable kernel only consist of small amount of patches, but not for 184.108.40.206. This version consists of a bunch of updates and bug fixes, which mostly are related to security. Why does this version contains a lot of patches? I don't know, but since Greg and Chris was busy with 2.6.18 and 2.6.19 in the last 1-2 weeks, it seems that the patches have been waiting to be released and when they decided that they had stopped the future release of older kernel, they start working on the current -stable kernel which also needs an upgrade. You can see the full Changelog to see what has changed since 220.127.116.11.
I skipped 18.104.22.168, since it only consists of 1 patch and i didn't think my system need that version, but i'm sure that i will upgrade to 22.214.171.124 (hopefully tonight). I hope the compilation won't take too much time. In my personal opinion, kernel 2.6.19 and 2.6.20 are faster than previous kernel (in case of compilation time). Perhaps it's because there were some deletion on some unneeded modules, such as OSS (here and here) or because they have fixed some compilation warnings/errors, so the compilers don't have to fix it during compilation.