Treating her differently because she's a woman doesn't make him sexist nor is it demeaning (I think this is what you meant). I realize this might open a whole can of worms that I'm reluctant to open. But, in case you had not noticed, men and women ARE different. They are not the same. They interact differently. This is why he probably did NOT do this to Blair's shoulders. Men and women interact differently. Two women interact differently. Two men interact differently. That's not sexism-- it's just the way things are.
Did you catch the link I provided before? Merkel clearly likes Bush. Unless she complains, well, I don't think it's anything at all. They are friendly. And, if you watch this entire video, not just the shoulder squeeze, you'll see that they are friendly.
http://video.google.com/videoplay?docid=4372463076604414221&q=merkel+bush
This is just all about Bush bashing, as it always is, all the time. This isn't that it's completely inappropriate that he gave her shoulders a squeeze. They shared smiles and a kiss earlier in the day (catch the video link I pasted), and they are friends. He did it in public because there's nothing at all to be ashamed of. Merkel LIKES him (yes, as hard as that is to believe for you!) and she is glad to have the relationship with Bush/the US that her predecessor did not.