Yes, but at the same time many people have dyslexia, so misspelling words like this is something very difficult to overcome. I have dyspraxia, and have a lot of trouble remembering where and where not to put double letters. I find 'Occasion' and 'Necessary' particularly tricky.
It does annoy me when people misspell anything. Lose and Loose are very common ones that get misspelled. I'm not sure why. The meanings are very different. I believe it shows a laziness when people cant be bothered to write and spell properly.
Since you asked Bryony I was curious had a search. Looks like it affects about 10% of the population, so about the same as in the UK. Sounds like it's a bit tricky to diagnose and can be mistaken for other things, so who knows really. http://dyslexiaassociation.org.au/what-is-dyslexia
It could be laziness, or just poor education (lousy schools, lack of parental support- not blaming the parents either, you can't teach something if you don't know it yourself). I was lucky enough to have parents who encouraged me to read and taught me spelling and grammar at home so I'd have been okay no matter what my schools were like, but not everybody gets that. Growing up I found it frustrating how much schools seemed to prioritise sport over academic achievement and science and maths over the humanities. Fitness is good and maths and science are important, but it would have been nice if there had been things like advanced English classes (maths classes were streamed into basic and advanced but English wasn't, so you had kids who could barely read in with kids who finished all their work early and had nothing to do, which benefited nobody). I imagine that kind of thing has had an effect on the general population's ability and motivation to spell correctly.
Yes. All misspelled words and bad grammar drive me bonkers. It's lucky that I don't carry a chisel tip marker with me at all times or I would be correcting signs all over the place. Oddly, fruiterers seem to be the worst.