Oh yes, it is totally a gimmick!
Back in 2008 when we were in the market for a new Vacuum Cleaner, and neither me or my mum were "in the know" about cleaners, so we went for the highest wattage cleaner we could afford.
Luckily it turned out well as the JMB SC1056 has been very reliable and has great suction, but we could have ended up with an overpowered screamer!
Luckily, these days, I know what I'm talking about, so if I did buy a new cleaner, I'd go for the higher air watts, regardless of the actual wattage.
The fact is though, that I'd sooner buy a 1980's cleaner than a new one, so I'll never have to bother about avoiding overpowered pieces of dirt!