Although I share your frustration, good luck finding some of Nikon's more popular glass in stock at a reputable authorized dealers. Generally speaking, Canon's supply chain is superior to Nikon's. The grass is not always greener on the otherside.
For me, as one who preordered back in February, this news is beyond inexcusable! Canon's photographic division must be completely inept. At this point, the ONLY thing keeping me with Canon is the TS-E 17mm. If Nikon comes out with a comparable lens, I'll switch in a heartbeat.
It usually happens for me, that the lane which I'm currently not driving moves faster. After I switch the other goes faster. But here you can be on two lanes at once, so why complaining? The story with Canon's preoders isn't such for the first time I suppose? What about the learning curve? As long as people will preorder so many months before the release, Canon has no reason to keep the announced dates. If people won't preorder once or two, then Canon for the third time will reconsider when to announce new stuff to appear on the shelves. I think, that preordering is like playing a roulette - if you are lucky, then you get one but if you have to wait, then you can blame only yourself.
People were waiting how many months for 1DX? How long after the first delivery was it available for anybody? Was it worth preordering? All those complaints about light leak in 5d3 I think came from people who preordered.
I really don't see any point in preordering AND complaining. If you preorder then don't complain, please...
people can and should complain all they want. canon says this is when your lens will be here. canon takes your money (and lots of it). you hold off on other things and make plans based off of when canon said your expensive lens will be ready. then, you don't get it.
so why shouldn't people complain? i'm confused? just because something tends to happen a lot doesn't mean you shouldn't complain. if there was a huge hole on a bridge, and it was there for a long time, should people not complain about so it doesn't get fixed? under your logic, they should just shut up.
i would think that people should start screaming bloody murder when they don't get this stuff. it will force canon to stop making these BS release dates, just to lock in customers. most software companies refuse to give release dates, because their are ALWAYS problems and dates get pushed back. they learned to only give a date when the stuff is ready - canon needs to do the same thing.
so i say, if you preorder and don't get it then complain, please...