It's hard to say.
I'm trying to look at it from a business perspective...
In May 2009 WoW held 11.5 MILLION subscriptions. At $15/month per subscription, they made $172,500,000 that month alone. If they maintain that number for one year, they would make $2,070,000,000. Therefore, why release competition against your largest income? I predict a quarter of WoW subscribers will quit WoW in favor of SCII and/or DIII, even if just for a year. (I say 25% because several people have more than one account that they pay for.) With most games going at $60, that's equivilant to 4 months of WoW subsciption. If a WoW user cancels their subsciption for just one year, blizzard will lose $120/person/year (if they buy one of their other games at $60). So it really doesn't make sense to release either game until WoW dies.