At a really really gross (and unfair level) I think a Developer thinks:
"I will put this button here because I find the asthetics pleasing and that is where I think it should go"
and a Tester thinks more like:
"Where should the button go?"
"Where does the user want it to be?"
"Is that the best place for it?"
"What does the usability manifest say about button placement?"
"What is the company's style regarding placement of buttons?"
"Should all users see the button or are there permissioning issues?"
"What does this button do?"
"What is it supposed to do?"
"Not every solution was derived to address an obvious problem" - Me (quite recently indeed)