Yeah, sure they are! If you are a Democrat from a right-leaning district, would you endorse the most liberal Senator in Congress? Why would you tie yourself to a guy who wants to raise taxes during a slowed down economy and who has no problem with higher gas prices:

The presidential race may be topic A, B and C in Washington these days, but some people are just too busy to think about it — particularly, it seems, centrist Democrats from conservative districts, who aren’t exactly eager to align themselves with Sen. Barack Obama.

Rep. Travis Childers, elected just weeks ago in a Mississippi special election, hasn’t endorsed anyone in the presidential race yet. “We have had our head down at work, trying to get our feet on the ground up here,” said Childers’ chief of staff, Brad Morris. “The presidential politics just has not been on our mind.”
Rep. Heath Shuler, a freshman Democrat from right-leaning North Carolina, has also been too busy to endorse. After Sen. Hillary Rodham Clinton carried his district in the North Carolina primary, Shuler said he would cast his superdelegate vote for her at the Democratic convention.
Now that Clinton is out of the race? “We’ve gone back to his work up there in the House,” said Shuler spokesman Andrew Whalen. “We’re not really too focused on the presidential [race].”
[…]
A spokesman for Rep. Tim Mahoney (D-Fla.) told Politico on Thursday that Mahoney will remain neutral. So will Rep. Jim Marshall, a Democrat in a conservative Georgia district. Marshall didn’t endorse Sen. John F. Kerry (D-Mass.) in 2004, and he won’t endorse anyone this year, either. “Jim, as a rule, doesn’t get involved in other people’s campaigns,” said spokesman Doug Moore.
Louisiana Democratic Rep. Charlie Melancon has yet to endorse Obama. Until Thursday, neither had newly elected Louisiana Rep. Don Cazayoux. “Since coming to office, it has been Rep. Cazayoux’s position to let the presidential primary process play out, which it has,” said Cazayoux spokesman Lewis Lowe. “Now that Sen. Obama is the presumptive nominee, Rep. Cazayoux looks forward to working with him to improve the economy and increase access to quality health care for all Americans.”