The key item to note in the article you point out is that Iphone mail will only operate in true push mode if the email account you setup on the Iphone is setup to use Exchange Active Sync. IOS4 for the Iphone introduced the ability to connect to multiple Exchange based accounts thus allowing you to setup multiple push based email accounts (again if your mail provider provides active syncing). I have my google mail, yahoo mail, and company exchange server all setup as push on my Iphone. I get my company exchange email in 2-3 seconds and the google and yahoo mail in about 10 seconds.
All the above being said I still prefer the Blackberry for mail because Blackberry delivers the mail over their own network and the mail is encrypted end to end for security.