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It's hard to prove a negative (i.e. that airlines never check), but I've never seen it happen. A couple of commenters have suggested they've never seen it either.
I have a 30 inch suitcase whose dimensions add up to 66 inches, if you include the wheels. There's never been any sort of a problem, and I've seen bigger suitcases used by others with no problems either.
As long as you stick with a typical wheeled suitcase I think you'll be fine. They might be more likely to measure the great big aluminium boxes I've seen a few people travelling with.