I work at an Office Depot store and we haven't had this said to us. It's not company policy and I don't personally do it, but we do get pissed when other stores send us customers who they know won't be getting a warranty. I've never had a manager tell me to lie to a customer about our stock unless we believed they were involved in some type of scam (rebate scams, etc). It's a moral decision made by the employee, not the company.
Personally I never buy a plan on any of my electronics because I'm a geek and get bored of electronics after the first year anyways!
Also, I never really cared much about the commission. We are always trained over and over on how to sell warranties, but never to the point that we stretched the truth. Like I said before, it's the employees fault for lying or trying to get a commission.
Most electronics come with a one year manufacture which is enough for most people and it's not like the plans are worthless. I've seen quite a few people that purchased cameras 2 years ago, come in with an Office Depot gift card for the price they paid and walk out with a better camera all for the price of the original plan (like 29.99, which is pretty damn good for a new camera worth $300).