yes, but are they barking up the right tree?
Canon Quality control isn't perfect, but when reading the forums, it always sounds like there is a huge variation in individual quality within the pro lens lineup.
I personaly do believe that a lot of those who complain do not a have a better or worse lens than others, but rather expect the impossible from their lens.
Of course, if you spend so much money on the lens, you can be critical for a reason, but spending ten times as much will not mean that the lens is ten times as sharp.
That doen't mean that every once in a while, somebody can have bad luck, as you apparently did, but I think the presence of "bad copies" is much lower than it appears.