I want to agree with you because I think it will be the iPhone 5 as well. I think it's perfectly reasonable for them to avoid 4S or 4G or 4GS or any 'complicated' naming schemes... but at the same time, I think the reason the second iPhone was named 3G was to emphasize that it had 3G. If the new phone has 4G it's not completely unreasonable to think they would want to emphasize it again (and vice versa, if it DOESN'T have 4G, naming it iPhone 5 would be a way of taking attention away from not having 4G).
The problem with naming it 4G is that the following year, it would be weird to jump from the iPhone 4G to the iPhone 6... and even weirded when 5G comes out and they're on iPhone 7 or 8 (just guessing) because they can't exactly go backwards.
I was actually thinking about this on my drive into work this morning. I'm wondering if they'll ever abandon the numbering of the mobile devices? On their website it just lists iPhone, iPad etc and then the pages it links to specify iPhone 4 or iPad 2. Having said that, the iPod Nano is just the Nano, the Shuffle is just the shuffle. On the forums we refer to them as 4th gen or 6th gen which gets difficult.. it's definitely easier to identify it as iPhone 4.
Their computers are just Macbook Pros, iMacs, etc.. but they have different revisions (minor and major) and revision cycles (the only minor bump for mobiles was the capacity of the original iPhone, right?).
I wouldn't be surprised to see it eventually just be the iPad or the iPhone but I guess if they're focusing on consumers, it would make more sense to just label them as numbers... after all, the iPhone 8 HAS TO BE better than the iPhone 7 or 6.