Nope, its not cheaper there, not even after you claim VAT at the airport, will probably still be slightly more expensive than what is offered in Singapore. Not a wise choice to buy in Thailand. You'll probably save more if you got one from Hong Kong instead.
Yes bro, you're generally right about the luxury items. However, some electronic products (non-branded ones) can be especially cheap in thailand, but the quality ain't something to shout about. For more well known brands, i would say you're right about the equivalent counterpart portion =)