There is a lesson for us to learn from this but it's not the one you are claiming. As Toledo points out there were plenty on here who wanted Moyes over Wenger.
Also, what is likely to happen now at Utd is that Ryan Giggs will take over, in the short term at least. There's no way they are going to bounce back with him in charge and as has been pointed out this could be the start of years in the doldrums for them.
The lesson for us is not to go down a similar route and dispense with Wenger in a knee jerk fashion, because we'd end up with Steve Bould as temp manager and in all likelihood, struggle to even maintain what we have.
The lesson is that replacing your manager is not an instant fix as some like to try and make out.