I agree Brown might have blown it, and I was highly critical of his campaign. However, Obama won by 23% in Massachusetts, and there is no way that any Republican over comes that. Brown lost by 7.5%. I think he would have maintained a higher level of respect had he at least gone down swinging the way he did in the special election.
The presidential year certainly added to it. Bill Weld lost the senate race in 1996 when two years before he had been reelected governor by the same constituency with 70% of the vote.