In my experience, the Thai restaurants around me (East coast US) like to make their sauces very oil/butter heavy, which contributes to the second phenomenon you alluded to. I've never been to Thailand, so I don't know if this is an exclusively American phenomenon or not.
I personally really like a good Lat na, but what I'm served is often noodles in a thick, chicken flavored grease (rather than stock or gravy).
Yeah ok sounds like a local "adaption" of the menu.
Even with a Thai owner and/or chef, it seems in most countries, there is some degree of adapting each dish to the local environment. This may be because of available ingredients or because of local tastes.
Thai people do love to fry things (both shallow and deep), but in my experience that doesn't necessarily translate into particularly oily sauces. In my time here I've once had a green curry that actually had a visible layer of oil (about 1cm thick) floating on top of the sauce itself, but that is definitely not the norm!
In terms of butter, that is very surprising to me. The only thing I've ever seen butter used for here is to fry fresh roti (which are then served with condensed milk and banana or chocolate or sugar or whatever you want)..
Peanuts and hot sauce/peppers? I realize that's not all Thai food, but a lot of people start with a dish containing those things. Like when someone says Korean food doesn't agree with them, having only tried the gimchi.
In either case, I can't work out how specifically thai food would make you do either consistently.