The correct answer is: No, campaigns that go beyond mid-level take more time, and thus even though they happen regularly, it isn't "often".
More seriously, looking at my campaigns since 3E:
Age of Worms - currently at 10th, will finish at 20+ (1 year)
Ulek II - currently at 6th, will probably finish at 15+ (6 months)
Living Greyhawk - currently at 7th, will finish at 16+ (2 years)
Mark of Heroes - currently at 8th, will finish at ?? (1 year)
Necropolis - finished at 15th (3 years)
Castle Greyhawk - finished at 15th (6 months - this was just fun!)
Key of Destiny - "on hiatus" at 7th (plan to finish at 20+) - (6 months)
Ulek I - finished at 10th - (1 1/2 years)
Feast of Xan-Yae - finished at 14th+ (2.5 years)
All campaigns above started at 1st level
Cheers!