To wend a bit of a middle path between Messrs. Klein and Chait, I think it's perfectly reasonable for an American president to say that he wouldn't have any diplomatic talks with Hamas as long as that's Israel's position as well -- after all, what would they talk about? Hamas can't make concessions to the United States nor is there much of anything the United States would concede to Hamas. So in that sense, Barack Obama's refusal to expand his generous meetings policy to Hamas is both defensible policy and a good cheap talk way of saying something that "pro-Israel" folks like.
The more meaningful question facing an American administration would be what kind of counsel/pressure/whatever they give to the government of Israel regarding holding talks with Hamas. The Bush administration, in line with their general approach to the world, has always signaled unconditional support for Israel's preconditions for dealing with Hamas, even though it was the Bush administration that engineered Hamas' rise to power. It seems to me that the reasons it's smart for the U.S. to, as Obama suggests, negotiate in a meaningful way with countries like Syria and Iran are roughly the same as the reasons why it would be smart for Israel to negotiate with Hamas without preconditions. Whether or not Obama agrees with that or communicates those sentiments to the Israelis is the more substantial issue.