Not suggesting that, rather that they are restricting production (or distribution) of the new, high-margin lenses to keep demand high and thus obviate any pressure for discounting that cuts into the margins.
That seems like a rather convoluted explanation of the stock situation to me. I imagine Canon would rather take the revenue and profit now instead of behaving like Rolex in terms of restricting supply (and people tolerate Rolex only because the market price for some watches are higher than the MSRP). This is especially true with the 100-300, which, like other superteles, will never be discounted in its lifecycle.
It seems more likely to me that the higher end lenses are more complicated and require higher precision manufacturing, and it is just more difficult to manufacture. To me, Canon would like to manufacture and sell more higher end stuff, but they just can't given current resources.