If people know they can't spell, you'd think they'd get it checked before it goes live/published. The fact they don't means they either don't care and assume no one else does; or they have no idea that they are crap at spelling.
Bad spelling and grammar are a particular problem for websites because of it being one of the ways of spotting fraudulent overseas sites. Unfortunately it is possible to get a .UK name and put a false address to look credible while selling fake goods or ones with worthless guarantees. I've had brilliant service of suppliers all over the world, but genuine ones have no reason not to be honest about where they are.
Useful weapon for secondary English lessons actually, as I know from experience (I work in a secondary school) just how bad some teenagers' spelling is, and it's likely that some of them may well bve interested in the idea of website design as a career.