OF COURSE their will be a 5th generation iPhone this year! You forget what business this is, the cellphone business. It runs on 2 year contracts and when people's contracts are up they want new phones. Not 1+ year old phones, they want the latest and greatest to justify their locking into a new contract so every phone company, Apple included, has to have a new phone at least once a year for all those folks to buy and feel good about buying. No one wants to lock in a 2 year contract on a phone that came out over a year ago!
Apple will continue to release revisions to their phone at least once per year, and this year you may see for the first time TWO revisions, a spring revision to the iPhone 4 that includes the GSM/CDMA chip to allow it to work on AT&T and Verizon followed by the iPhone 4/4s/5 whatever they call it in the June timeframe that includes other hardware changes (better cameras, perhaps a 4 inch screen etc.)