I think the reason they haven't updated the 50mm 1.8, is because it is so cheap and cheerful and sells by the bucketload just as it is.
If they did update it, it's cost would go up by at least a factor of 2, and then the sales would plummet.
Updating lenses means new tooling and new systems to manufacture it, and with the older lenses, you are paying for yesterdays tooling costs, and not today's, which would be significantly higher.
Canon need some low-cost lenses in its line up as not all DSLR users are prepared to pay for L lenses and I would say that the greater majority of their lens sales are the cheap, kit lenses anyway.
Ask any camera retailer which lens sells in the highest volume, and they will tell you that the cheaper lenses outsell the L glass by 3 or 4 times, both in volume and $$$ sales.
It's a bit like cars.
We all want a super high performance, gorgeous looking car, but most of us drive smaller, cheaper cars.
Don't forget, we are on this forum because we are real enthusiasts, and enthusiasts who are prepared to spend big money on stuff are only a small part of any consumer market.
if is not broken, don't fix it.
Yet, a large percentage of enthusiasts still are driven by the mega-pixel race, and pixel-peep of every shot they take.
Some of my friends have no problem spending $200 on a new phone that will be outdated in a few months, and then will be looking to replace with a new one at great loss.
With lenses, once you buy quality - that you need and use - it's a keeper. You don't really need to update just because a new version is out.
If indeed a lens is an underperformer,, then most likely you already got ride of, or you never got it.
The average Joe, considers a lens above $500 already very expensive...yet, has no problems in paying over twice that in G4 phone/ wireless internet access charges
Priorities...that's a bitch
Canon's prioities: stay alive and make money, whitout loosing position in the market/ratings
For me, a product that needs constant update, just means was not done right to start with...