If they only made 9 mistakes in the I don't know how many years they have been in business they are doing awesome!
1) killing the print editions of dungeon and dragon
Magazines have been slowly dying. The PDf versions that we have now are still awesome. I think this is a win.
2) lots of thinly veiled insults at previous editions, fans of previous editions, and certain playstyles in the hype leading up to 4E
I didn't see this. I still play 3e and I talk to Wizards people and they don't seem to m ind that I do. Don't confuse marketing with insults. That might be the issue.
3) hyping a product that will never be (virtual table top)
Sometimes things don't work out. While it sounded cool I can't say I'm missing not having it.
4) the GSL
I'm not sure its a mistake. I think it is doing exactly what they wanted.
5) laying off D&D employees every six months even though 4E is supposedly doing great
Businesses cut back even ones in the black. 4e doing great can mean a lot of things and there is a lot of behind the scenes decision making that goes into hiring and firing personal.
6) designing the newest edition around an excruciatingly slow combat system that makes playing the game almost unfeasible
That's just your opinion and nit a mistake. 4e works fine for plenty of groups. Not for everyone sure but no game does.
7) stopping legal sales of all pdfs
Again, maybe a mistake we don't know all the facts though.
8) an astonishing amount of errata and rules updates that invalidates physical books very quickly and is nearly impossible to keep up with
Hasn't been that bad in my mind and with the DDI it is cake work.
9) killing DDM which has resulted in nearly killing the entire minis line
Minis are still being made, not sure how it is almost dead.