This is a specific facet of a more general rule of public speaking: don't apologize. It has nothing to do with your presentation, and it's likely the audience wouldn't have noticed, anyway--so why point it out?

There is an exception to this rule, though: if the condition is A) painfully obvious, and B) out of your control, you can apologize. Examples: air conditioners in room broken, or jackhammers next door. But don't apologize for your own stuff; that's just tacky.