Beck is a useful idiot of the leftist media in this regard; Beck's (I would describe over-the-top) criticism of the GOP at CPAC allows the media to portray the voter/electorate discontent as one that is aimed at all politicians, not just Democrats. Beck's not smart enough to understand that his theatrical and grandiose criticism of the GOP is what will be the next day's soundbite - he talks for an hour or more, but it's the :20 second soundbite of him laying into Republicans is what gets played over and over again. This is what Bennett, and in his own way Levin, were attempting to address.
People aren't mad at incumbents, they're made at profligate spending. But, Beck's rhetoric allows the media to portray it in the exact opposite way. Is this intentional on Becks part? Only time will tell.
Are you saying they aren't made at any Republicans? Then why is McCain facing such a hard race?!
There is plenty of voter discontent pointed at both Democrats and RINOs, which make up more of congress than true conservatives.