I agree that they probably wont sell - to turn down a bid 18mil shows that they want to keep hold of him, or maybe it shows they don't want to sell him to fellow relegation strugglers...Either way I can't see him leaving this Jan.
As for him not being one of the best strikers in europe. I would argue with that. I would say that he would be one of the best strikers, that are actually available. Sure, he's no Eto'o, but Eto'o won't be available. It's pretty obvious that Bent will be leaving Charlton pretty soonish, and I think with his premiership experience, his goalscoring record, his age and his availability we should try our hardest to get him. Letting him go to another team would, IMO of course, be a big mistake.
If he went to a Spurzzz kind of team it would make them stronger than us and if he went to one of 'The Big 4' (TM Sky Sports) it would push them further ahead of us.
With, apparantly, all the transfer fees to go through the roof after the new TV deal kicks in, I wouldn't consider 18-20 mil for Darren Bent too much money.