I think 2005 defined the maturity with digital... thats when I got my 20D and I felt that I had finally replaced my film camera. Id had a digital camera since 2001 but never really felt it replaced film until my 20D. Also at that time, I think we were hitting the resolution threshold of 35mm film so lenses had to change. Plus if you look at the emerging technologies of that time: IS, the technologies needed to achieve IS with f2.8 and F4 continuous zooms and primes, the glass technology required for this and how many people feel confortable with zooms when primes previously were exclusive. Keep in mind, the whole time, the image sensor has gotten better and better. Less of the lens artifacting could be hidden by the imaging system (film or digital). So what we as consumers are receiving as an end product is a lot of value.
Oh and its still made in japan, it hasn't been sourced to a cheaper labor pool. So your money goes to supporting a japanese worker standard of living.
My humble F1.4 50mm is still around and is on its third camera body. Thats value. I never regret the price of a lens as long as it fulfills a need and I didn't just get it to get it. That wouldn't be the lenses fault but mine. Luckily I research a purchase like a madman.
Take the 5D3.. a $1000 markup from the mark2, which was cheaper than the mark1!. But what did we get? The AF from the 1DX minus the contribution of the 100,000 pixel AE. "Baby 1D" functionality and build, while the 6D fulfilled the bracket that the markii had previously but with better IQ.
Look at the changes at the xxD product line: 20D-50D were the semipro models until the 60D moved into the "super rebel" realm where we lost the joystick, mag alloy body, etc... So to get the evolution of the xxD model line, which used to be ~$1300, you had to get the 7D which was now in the ~$1800 range. In other words, to get an upgrade in the xxD model range, it cost $500 more! Now with the 5D, same thing.. the 6D gets you a full frame super rebel, and to get a feature upgrade (they way we did from 20D-50D), you have to pay like $700 more for a 5DmarkIII!
Same with lenses, you want to get the successors to the 16-35mm, 24-70mm, 70-200mm, you are paying at least $700 more!
The flip side to this is that there has been a demand for these products and more people are monetizing their photography.