Andrew, I can see the logic and in a similar vein, it's often been my belief that 'Frequent Flyer Clubs' should be renamed 'High Spender Clubs' or 'Corporate Flyer Club' and that would make clear to those of us who scrimp and save points just to make Silver, than in fact we aren't really the target market of schemes like BD's Diamond Club or BA's Executive Club, for example. It's all about getting customers to part with huge sums of money. Yesterday I flew LBA/EDI and back on a company negotiated fare of £266 inc. taxes for a C ticket. What?! Would any sane person really pay this for a half hour flight each way? I could have travelled to New York for less than that.
The only people who prop up these clubs are those who fork out massive sums of money for a shiney looking card and some free pretzels before their flight. Corporate travellers of course.
Just think of how impressive it would look 'Welcome to the High Spender Club Lounge' or 'We'd like to extend a special welcome to our High Spenders'.

The more favourable alternative and to get rid of this 0.25 and 0.50 points for different fare types nonsense is to have a genuine Frequent Flyer Club. This would be based entirely on the number of flights flown, regardless of class, and would drag those who've wandered to Ryanair/Easyjet etc. back to bmi. I must admit that if I ever fly somewhere and am paying for it personally, I do shop around and do consider the LCC alternatives to the likes of bmi/ba. Do you think I would do this if I got 1200 points for a single sector with bmi? No way! I'd stick with bmi 'til the cows came home.