If you'd said £89 Halfords bike with steel bits, cup and cone BB and headsets, I'd agree with you; but by the time you get up to £250, most of the parts are aluminium, so no rust, and they have cartridge BBs and headsets. The Boardman is a bit more highly strung with lighter weight components, so I don't think it's true that it'll last any longer.
I don't see anything on the Woosh that'll make it last any less than any other bike except maybe the rear derailleur and gears, which is easy to replace and doesn't cost very much. It wouldn't surprise me if a £3500 Bosch-motored bike with a rear derailleur wouldn't last any longer due to the lighter weight and higher power, and they'd be very expensive to replace.
Electric bikes are like hifis, You can pay not too much and get one that'll play all your favourite tunes, or you can get one for a lot more money, which probably sounds better, but it doesn't make the song any better.
For some people, it makes a difference. Some people have iPhones, Macbooks and designer clothes, others have Samsungs, Medion laptops and clothes from Asda. There's no justification one way or the other, it's just depends on the way you are.
If you want to be happy, never buy something you can't afford, and never borrow money to buy things.