and fair enough, for the maybe handful of lenses a month they might sell on the high-priced half of the range (300 f/2.8 I, €4500 and up). Margins might be fairly good, but just the outlay for keeping them in stock and the extra security in the shop adds a hefty price tag.
I'd be surprised at any shop stocking them, really, unless it's a really popular shop in a rich city with a massive (US-sized) city population, lots of tourists, and/or good sports/nature nearby (ie, something like Hong Kong or Singapore).
And also, there's not much range in the upper-most price bracket, not the kind of thing you buy on a whim, spending that much you should research a lot first, buying online from a central warehouse is the only way that makes sense...
For the lower end of the range, up to the 28-300L (€2500), they'd churn through them a lot faster, and can afford to keep a few of each in stock at a time. also, there's a lot more variation the cheaper you get, having staff that can talk you into the next model up is a lot more possible in a real store...