There is plenty of evidence to say this is false.
Many attacks on IE find weaknesses in features that are unique to IE, such as ActiveX, which don’t affect other browsers.
There are also difference in the development and security release cycles and target audience that mean bugs may be sat on for longer leaving the browser open to attack.
Like Bob, you’re basing you arguments on ideology rather than looking at the evidence.
There’s also pretty strong empirical evidence that hackers find IE easier to hack.
http://techhamlet.com/2011/03/pwn2own-2011/
Not to mention that with Firefox having acquired 27% of the market, Chrome 16%, Safari 7% and Opera 3%, we should be seeing more vulnerabilities found in these browsers- where’s the evidence for that?