so you say lenses are different to:
why do we have 10-20 year old optics but not printers, cars, cpus or handys?
of course you can not improve optics as fast as other technology ... but all these things cost R&D too. your argumentation has a hole i think.
imho canon is not producing new lenses because they don´t have the competition.
You've proven my point masterfully
The difference in lens technology/quality has not forced any of the dominant manufacturers to update all of their lenses on a regular basis because the technology advances (and competition) don't require it. Cars, CPUs, cell phones -- all of these evolve on a monthly basis. Miss innovation and you're out of business quickly (Blackberry, Nokia...)
Canon absolutely has competition, and has actually been reacting less quickly than some might have thought. No one thought the Sony Alpha series would take off, but Sony does have (or used to have) a reputable name as the leader in consumer electronics. Nikon has made HUGE inroads in the last 3-4 years. Canon has innovated its long glass as best it can, but Nikon has done a better job with camera bodies (my personal view.)
To say that Canon isn't producing new lenses because it doesn't have the competition misses quite a bit. Canon is very worried about Nikon -- just look at all the dark lenses on the sidelines of major sporting events now, when 5 years ago they were all Canon white.
The R&D process is arduous -- look how long it takes for patents to make it into actual lenses (and often times they never materialize because they can't be produced in sufficient yield with proper quality. This is the case with all camera/lens manufacturers -- I'm just highlighting that it takes time and it's hard to react quickly to competitors when tooling a new lens takes years.
In full disclosure, I have good knowledge of Canon Japan's corporate team. Nothing I've said here should be shocking to anyone; just a reminder that Canon is fully aware of customer desires and will deliver as soon as they are able. Believe me, they want to sell you a newer, more expensive lens as soon as possible!