I really want to check the posted URL and be sure that it points exactly where I want, and doesn't reveal anything unnecessary (all those URLs with tons of information after '?'). I'd feel very embarrassed if I had posted something spam-like. And it's not that hard. Just use some desktop twitter client, copy URL there, copy it back to the browser, try it, make some corrections if needed, and that's it. It shouldn't be that hard.