This doesn't explain why the full service retail outlets - important ones - which still operate in North America have been experiencing procurement issues.
Never claimed it was the only reason, just one. The situation in Japan will have an effect on supply for some time. (As most Nikon stuff is out of Thailand, not sure why they are impacted to any great degree)
I spend two days a week at my account, one of the last remaining full service shops in Northern California. It's 'hanging on by a thread' and has a doubtful future, partly because of management problems. However...the main impediment to it's continued existence is the notion that any B&M retailer who dares try to operate at a profit is a "ripoff". The businesses who do run a successful physical presence are the ones who have learned to adapt quickly enough in the etail realm.
Every day, the scenario is much like this - Customer comes in, spends an hour or so fondling expensive gear, when given the price become indignent and proclaims at top of voice that they can get it for so-in-so online, and walks out in a huff(And of course they wanted a discount for the display product) Now spends hours online asking what lens, bag, tripod, etc. they should get 'cause there's nowhere to go and actually handle one. Often they find out too late that their "deal" is grey market and then grouse that it's unfair that there's no warranty, or can't get it fixed if a Nikon.
Bear in mind that the margins on cameras and lenses is about 10%, so the store is making about $150 on that $1500 lens...if you buy it. Gotta sell a lot of expensive stuff to keep the doors open. The margins are better on accessories and such, but not so much as the old days. The main profit in the pre digital era was film and processing(usually what made the operation worthwhile). That's gone now, so now the equipment and accessory sales are vital to survival.
So far, the working professional(or wannabe) has been a saving grace at the store. Being one of the last places with a selection of studio lighting, backdrops, and high end gear, when something breaks, or they need a mission critical piece, there's a good chance we have it. We also do inhouse repairs, and can often get their stuff back to them in a couple of days or so. And I often figure out it's pilot error, and send them off happy at no charge. Most manufacturers charge a full repair price even if no problem is found. Have seen many $100+ clean-and-checks.
When the place shutters, wonder where they plan on going.