after reading that article I don't see how it supports the statement that 4.3 must be downloaded for security reasons.
what's the connection between the bug mentioned (exploited in a competition) and any fixes in 4.3?
Here is the full list of security fixes made to iOS 4.3 that can get you infected just by viewing a web page: http://support.apple.com/kb/HT4564
Note the huge length of the list.
There are also many more vulnerabilities that Apple has not fixed yet as shown by Pwn2Own, but it is better to have some security fixes than none at all.