Reread what I wrote, I said Android and iOS. I didn't say anything about Windows, Mac, Windows RT and WP nor did I say that Office 365 is all that's needed.
You said "Why would they port Office to Android and iOS when you have Office 365 on those devices." Let's examine the logical steps - please tell me if I get any wrong - preferably with the number of the point where I misunderstand.
If I understand your logic correctly...
1. There's no need for Microsoft to port full Office to iOS and Android, presumably because Office 365 provides everything users of those platforms need, and cannot be improved upon by a full native client. If this wasn't true, there would be a point to porting full Office to iOS and Android.
2. Therefore, Office 365 must be as good as full Office on tablets and smartphones.
3. Therefore, Microsoft can drop full Office on WP and WinRT. Why would these devices need full Office when Office 365 is just as good?
4. OK, I stretched this a bit to say that full Office is also therefore pointless for Windows and Mac. I suppose it might be the case that on PCs and laptops, full Office still offers something above Office 365. So you got me there - I was wrong!
But it's good that we identified that full Office is not needed on WP and WinRT. I assume Microsoft will now stop developing it for those platforms and save some money!