Apple certainly won't accept bitcoin, especially not in the near future. They seem quite serious about their Apple Pay system. Bitcoin is pretty much their enemy right now, i would assume.
Microsoft has taken some VERY strange steps lately. They seem to make some big changes, and i really like them. (open source .NET for example)
Perhaps this move to bitcoin is another step in their big plan to change their stategy.
I can see google taking the step, but then again, i find google quite hard to predict sometimes.
When I see how many Google-employees are trading Bitcoin privately, I wouldn't be surprised if they build a lobby within the company for supporting BTC....
It does not work that way. They have smart people dedicated to looking for trends and technology opportunities, then they make a decision on higher level. I am pretty sure they have already considered it. They just don't see the potential, plan something on their own or do not think that it will fit their business model. Or just wait to see how it goes before making a decision.
Personally, I think that they are trying to snipe some promising startup, just haven't really finalized anything.