Oh come on. While I absolutely agree that Linux is more secure and generally a better idea to use it, this could not have been prevented by using Linux.
Your wallet.dat is in your home directory, in the .bitcoin folder. That means it is freely accessible by any binary you run. All it has to do is grab that file, and ftp/email/something else it to someone. That is all perfectly possible, even from a severely limited Linux user account.
Supporting Linux for its features is all fine, but don't go run around like a blind fanboy, saying the entire world could be saved by running Linux.

Bullshit. A wallet.dat with a password (and said wallet.dat never touching the disk in unencrypted form) prevents outright stealing of a wallet.dat file, as you would need the password and/or keyfile to unlock it. That means that simple hit-and-run wallet.dat stealers are practically useless.
This is also why third-party encryption is practically useless. Either your virtual disk with wallet is mounted (and it can be read off said disk as if it was never encrypted, doing a simple filesystem search) or it's not, in which case you can't use Bitcoin. Having to decrypt the wallet every time you want to use it (and thus leaving an unencrypted copy on your hard drive) is not an option either. This is why the client ITSELF should provide encryption that only happens when the wallet is actually needed, and that doesn't let the unencrypted wallet touch the drive, ever.

And what if your server is compromised? Exactly.

Screen flickering and/or hiding the numbers/letters when mousing over them (funnily enough Runescape uses a system like this for their bank PINs).

There have been proper free antivirus solutions for years. The problem is that the antivirus solution offered by Microsoft is really only a patch to something that should have been prevented before. They should have made a properly secured architecture for Windows from the very beginning. Look at it like this: Linux uses a condom, Microsoft relies on the morning-after pill.