oh that recycled tabloid cliche again? you definitely have a deep understanding of our culture. we love "plucky brits" and underdogs.
Yes, you love him whilst he's winning, then he loses and gets trashed in the papers and by British fans that he's a hack, a failure and the like. 50% of Murray's mental fragility is the weight of expectation upon his shoulders, much like it was with Henman. It was always predictable each year to watch Henman fail in the semis.
I don't think anyone who actually follows tennis regularly over here actually expects Murray to win Slams. If they do they shouldn't. It's more the people who tune into Wimbledon each year and support Murray because he's British who, more so the ones who go along who put the pressure on him. The journalists do it more in hope than expectation, then when he loses like he has in all his finals and the semi finals at Wimbledon, they tell it like it is that he was outclassed, which has been true in all his defeats at Wimbledon against Rafa & Roddick, plus the Slam finals where he's never even taken a set. He's just not as good as people want him to be.