This is one of those title says it all posts, but I'll elaborate: the fact that there is neither a new class nor a new race in Warlords of Draenor isn't a problem. First up, there's the obvious fact that we're getting redesigns for the eight original races plus draenei and blood elves. In terms of art design, that's an incredible amount of work, far more than designing one or even two new races. Racial abilities for each race are also being redesigned, meaning each will play differently. Moreover, by not introducing a new race or class, we don't need to have a starter zone designed for them, meaning that content design can focus on content for the 90 to 100 player, especially since thanks to the level 90 boost, it can be assumed that anyone who picks up Warlords and wants to play it can.
As has been said elsewhere, new races and classes are not content in and of themselves. They consume time and development resources to create them, and often they have content associated with them, and that content is usually only playable when you create one of them (although the monk did not actually get that treatment - save for one location in Pandaria that offered monk only quests, as a kind of home base, monks didn't see the death knight starter zone style experience) but by themselves a new race or class is just a different way to experience content. This is not to say they are not important. New classes offer new gameplay options, new abilities and spells, and sometimes new roles for players who did not enjoy, say, tanking or healing on previous classes.
But I think it's fair to say that World of Warcraft doesn't need the added complexity of three new specializations to balance right now. There's going to be a lot of work needed to balance out new spells and abilities, adjust item levels, change the way healing works while ensuring it does still work, implement entirely new gameplay like garrisons without also figuring out how to keep another class in the mix with the other 34 specializations we already have. Similarly, while I mourn for my alliance ogre paladin and horde arakkoa druid, do we need two more groups of racials to balance out?