Right, new terrian gen is new terrian gen, so they wont be updating maps at all.
Anything they can say in a livestream they can write down, either the livestream contained the information you claim, or it didn't. You cant claim to have heard information that doesn't exist.
Why so mad?
The mod pack is beta; things can and most definitely will change. Such is life in beta. The people who know exactly what changes the mods will bring to world gen are Eloraam (blog is down, twitter info is lukewarm... she doesn't update by the minute, so it's ready when it's ready; she's also been really busy with RL) and Azanor (have you seen the size of his
information thread... he updates frequently). From experience with previous mods and mod packs, the easiest solution is also the simplest; don't get attached to what you do yet but remember the seed if you like the world.
Slightly more involved solution? Don't explore too much of your map (minecraft will generated new chunks based on world gen it has, so by waiting to generate those new chunks you get a chance to generate stuff you missed... of course, I could be thinking of Bukkit there since that's what we did for to add jungles/emeralds to an existing popular server....) or be prepared to go leaping into books (seriously, MystCraft makes multiverse solutions easy....). It's really not all that much of a hassle if you're so attached to what you've done so far you don't want to just reset the world.
Finally, when did they make the rule that anything they say in live stream they should write down? Often times, they are either working (for free, btw, on the their mods or packs... to add features or squash bugs... many have a real job that actually pays their bills...
free hint - not the live stream) or blowing off steam by playing a game while chatting with their friends/fans. Neither activity lends itself well to self-transcribing every word that may leave their lips that may or may not seem important. Honestly, they have better things to do (like work) than to go back through their own content to write those things down. If someone wants to watch through DW20's youtube stuff and/or Slowpoke101's archived live streams and transcribe all of that... power to them.
TL;DR - World gen changes happen. Either be prepared to reset your world or generate new terrain/ages.