The problem is ALWAYS the people. Between malware from using pirated/hacked software to novices who don't know what they are doing by accepting anything on their computers to opening files from people they don't know [or do know but didn't find it the least bit suspicious].
In the case of Android it has also been Google for failing to properly secure the OS from this crap. Google Android OS is their version of Windows 95.
Apple has it right with the App Store (TM) but their pricing policy is rediculous.
Think of WinPhone is what the Mac was a few years back before the OS X started to get malware and other infections - relatively "clean" because it had a minority stake in the market share. In addition, unlike WinPhone, the iPhone also is a status symbol where malware writers will go after because they are sometimes rich[er] and sometimes dumb[er].