Very few vowels? Tongue in cheek for sure but just for the cheap seats: there are many vowels, some with awkward soundings totally unfamiliar to the western ear. Vowels are long and short versions, change tone depending on the consonant class, change tone again with the addition of a tone marker, change tone again with the prefix of a high class H consonant, change tone again with the prefix of the aw ang and consonant, change length with the addition of a certain character and can appear in front, behind, in the middle, above or below the word.
I agree to learn Thai it is best to learn the alphabet because all the info is there. It is not impossible to pick up with practise... the app Pocket Thai Master is very good. Neeranam's 'Let's learn one Thai word a day' thread is also worth a look.
As to should expats be able to speak Thai? Totally up to them and also depends if you live in a touristy place. I would, however, say you don't really know what's going on unless you can have a basic conversation with Thai friends or strangers. I'm way off fluent but make some sort of effort to converse with the locals of my adopted country.