It's one of the reasons that led to our support for the “do not call” list. Unfortunately, the telemarketing community has not comprehensively self-regulated. Those who conduct it ethically and according to the rules are paying a price now for those who have not.
It is my understanding that sequential dialing is not frequently used, at least certainly not on major national campaigns. I can't speak for small local businesses, but it's inappropriate to take a series of numbers and start sequential dialing. You never know when you're going to hit the intensive care ward of a hospital, amongst other things.