I think it's because this wasn't "news".  Overstock announced it would be accepting bitcoin payments weeks ago, and at that point it DID boost the price.

The thing to look for is whether this is successful or not.  If the merchants that agree to accept bitcoin end up seeing very little reward and give up, it will ultimately cause major trouble to bitcoin.  If the exact opposite happens, we'll see even bigger merchants hop onto the bandwagon. 

At this point the success of bitcoin entirely depends on people using it.  Even if it's just a small percentage of your bitcoin, buy stuff with it.  Or, if you don't want to lower your bitcoin balance, like me, buy stuff with it then immediately replace what you spent. 

If you have bitcoin and you aren't spending any of it, you are not helping the cause whatsoever, and ultimately just hurting yourself.