The thing is, there are plenty of states that don't get polled enough, while a safe Republican state like Kentucky has been polled 10 times. States that have been polled fewer times:
Colorado- An undeniable swing state.
Nevada- Again, an undeniable swing state.
New Mexico- Ditto.
North Dakota, Montana, Alaska, South Dakota, etc.- Some polls have shown Obama stronger than normal in these states, but we've had so few polls, that it's impossible to tell.
South Carolina- Only one poll here, showing McCain only up by 3. I'm not saying poll South Carolina every week, but some follow up here would be nice.
Indiana- Polls showed this competitive in April, but since then we haven't gotten anything.
New Hampshire- Again, undeniably a swing state.
Maybe the polling companies are testing the key Senate race where Mitch McConnell might lose in a Dem year and are waiting to start polling general election presidential matchups until closer to the time?
Personally, I agree that it would be preferable to see more swing-state votes, but financial incentives might be a cause here.
Yeah I remember when they did a slew of polls in Oklahoma in 2004, IIRC it was the closeness of the senate race there that was the reasoning behind polling it so much.
Of course, if you're calling people up to do a U.S. Senate poll, you essentially get the chance to do a U.S. President poll as well. You almost have to—it's key crosstabs information.