I've worked out why El Reg has no subscription option
It's like this.
1) One commentard is worth, say, £10/year in ad revenue.
2) Many commentards start paying £10/year in subs
3) The remaining commentards are therefore not inclined to spend £10, and are thus less valuable to the advertiser - if you care about IT enough to spend £10 reading it, you are a good target for IT ads.
4) The remaining 'tards are now worth only £5/year.
5) El Reg's revenue goes down.