why Google returns different number of searches estimations based on the word order, while Yahoo/Overture seems not to. Does it matter?
I'm not sure, but my guess would be that if Google is returning information based on word order, they probably have some part of their algorithm dedicated to word order. And that makes sense to me. Word order can be very important when you're looking for something and it could definitely mean the difference between finding something or not. So it makes sense that Google would care about word order. Of course, their algorithm is secret, so no one's going to be able to definitely comment on your question...except maybe Matt Cutts.
Yes it does matter for SERP ranking. And nobody care for Yahoo or MSN May I suggest that when you are deciding what Google phrase you are going after, look it up in Google Adwords Keyword Tool. It will return which of the scenario will have the higher searches. That is the one (order) that you go with. And if you link's anchor text is out of order with it, it will have a negative affect.
Yes in Google key phrase word order is important in SERPs. I am not agree with nobody care for yahoo and MSN. If we are not using Yahoo and MSN SEs it does not mean that nobody using.