Blizzard stated even before the release of Wrath of the Lich King that they wouldn't allow flying in Northrend till the higher levels, because they wanted people to experience everything, instead of just grabbing a quest, mount up, auto-fly while going on Youtube/Facebook/etc, get back on WoW, kill mob, mount up, fly back.
With this change, you are forced to level one character to 77 without being able to fly in Northrend, but after that you can make all of your level 68+ alts fly there, thereby saving an awful lot of time(I can't recall how many times my Warrior alt got mashed in New Hearthglen).
People who whine about this is the same who whine about boss nerfs, Mount- and the Emblem changes. Just because something becomes easier for others, doesn't mean you've been cheated for anything. You level 10 characters to 77 before you could fly? Congratulations then, you've got 10 80's before anyone will be able to fly there at level 68.
I, for one, will sit back and enjoy as my next alts fly away from those pesky Scarlets without anything they can do about it