As for IBM, its market cap is quite close to Microsoft, so I think they did reasonably well (they could have done even better if they've bet on software earlier, but that doesn't mean they should necessarily "bet outside their walls"). Also, the fact that they invested everything they had on an "open" platform (the PC architecture) is kind of an agreement to what you said they should have done... No?

As for Twitter, I find it funny that people see it as such a revolution. I mean, it's just a little social network with a very limited scope and features... I don't jmagine it revolutionizing more than it already does (it's a great outlet for the media, celebrities and breaking news, but I don't think it's sooo much more)... Or is it? :)