First off, I completely agree that "fan service" is no excuse for poor writing and that your last sentence is dead on. That said, if you think that sex doesn't sell or that this only happens to female characters then you aren't looking; how impractical would it be for a superhero who regularly gets shot at, flies at speeds capable of exit velocity, re-enters the atmosphere and much more, to wear nothing but jeans and a t-shirt? Well guess what! DC has just that and he is even related to our heroine, his name is Superboy and he seems to get his shirt ripped apart quite often, exposing his perfectly chiseled abs, chest and arms (ain't that a coincidence). Another perfect example is Nightwing, if you want a drinking game that might kill you (assuming you are 21) then pick a volume and for every gratuitous butt shot take a drink, pretty soon you wont be able to read for the night, or stand up straight for that matter.
While we're at it, remember when DC gave Wonder Woman pants and a Jacket or how Power Girl got a full coverage suit? Didn't last long did it? and male fans weren’t the only ones who complained. Also, if you want a lol then I recommend reading some of the hate mail girls sent to DC when Dick Grayson became Batman and butt shots stopped for a while.
The main difference is that when female characters are over sexualized people throw a tantrum but when the same thing happens to male characters no-one notices and no-one cares. But before you think I am ripping on you please remember the very first sentence I wrote. Also, I agree with you on Starfire's outfit, but lets be honest, she has never had a modest sense of dress throughout her entire comic book history... personally I don't understand why they didn't use her teen titans cartoon iteration, it was the most fan and critic loved version... not "edgy" enough I guess.