It's not overreacting. Even if it does come down to a provably unintentional glitch, any company that lets that kind of glitch get out and stay out for long enough for the internet to mobilize sucks.
I'm a software quality engineer. I do this sort of thing for a living, and I'm, if I may say so myself, pretty damn good at it. No, I don't work for a company as big as Amazon, nor is it in the same area of business. But I know what goes into the nuts and bolts of sending something out the door, and there is no justification for that level of failure.
The fact that they may have run an update on Easter weekend may make sense -- I don't know if that's a slower or faster time for shopping online. But when you roll an update out during dead time it's because if everything goes completely kablooie you're pissing off fewer people. Not because you think people won't notice the changes.
And I've worked in tech support, too. Yes, you have canned responses. But there's nothing justifiable in sending out disinformation. "We're not sure, we're looking into it, here is your ticket number and we'll call you when the people who actually know what they're doing have recovered from their Cadbury Creme Egg-induced coma" would have been a perfectly good canned response.
Software is hard is not an excuse. Not for a software/web service company. Amazon made their empire on understanding the way the web was going -- failing to understand where it has gone and how it will react to this kind of crap can take it down. Fix it and apologize, sincerely, ASAP, and those of us who like the convenience of Amazon will come back, even if we grumble a little. But you have to mean it, and you have to do it NOW.
 There are people reading this who know what company I work for. Please keep that information out of this and any unlocked post.