Thats why we do not see a whole flurry of upgraded high end lenses. The cost to develop and tool a new one is high -really high! The 24-70mmL and the 70-200mmL had to be done, and they sell in large quantities such that as soon as tooling and development is paid off, prices will drop.Actually, Canon likes to sell lenses, not have them priced so high that they do not sell.
If you ever meet some Canon exec, please be sure to tell them that - I wonder if they aren't being a bit too excessive even with the newest "standard" lens prices for their own good.
Many wish for a new ultra wide zoom, it will cost a lot more due to fewer sales, but it needs to be done as well. There is really no reason to put out another high priced lens, sales are in a tailspin as it is, the 24-70mm L MK II will be dropping in price soon.