Oz: personally, I agree that TWR should send the 2nd aircraft around. However, real world without automated alarm functions? I've seen many occasions when it has not been done.
Approach/Director ATCOs should be criticized for loose spacing, especially at a unit that is busy, however that .9 is the issue isn't it?! Hit the minimum spacing, be it 3, 4, 5 or 6miles and you get a pat on the head. Lose .1 of a mile and you're in the smelly stuff... for something which is in part out of your control.