Really? I'm guessing that he probably did have clearance for that. What was his clearance, and how do you know?
Now, Wilson didn't have an intelligence background. Indeed, the committee revealed that Wilson didn't have a "formal" security clearance, but the CIA gave him an "operational clearance." The fact is that there was little to recommend Wilson for the role, other than his wife’s persistence.
Now, this addressed his "clearance" while he was on the trip to Niger, I imagine. But I don't know what job he would have had in the government in 1998 when he married his wife, or why he would have known to check her status back when he might have had such clearances.
Wilson isn't cavalier about his wife's employment -- usually. He often says he can't answer questions, but it seems more of an act. When you get on national TV and say that Karl Rove should be frog-marched out of the White House for outing a CIA operative, it is hard to later claim that you never actually SAID she was a covert agent.