While from a financial standpoint this would make sense, most of the guys making the executive decisions at Apple are design focused and oriented. Dropping the headphone jack differentiates Apple even more from its competition, makes the phone sleeker, helps with water proofing, makes the wireless headphones more appealing (which not only act as headphones but also communication devices). This was much more than just a financial move for Apple, and in my opinion it looks to be a smart one.
For me i estimate my iphone use as:
80% Music 8% Calling 8% email 2% browsing 2% other stuff
With that in mind removing the 3.5 jack does not make the phone sleeker you need to see the adapter as a part of the iPhone as the phone is mostly useless without it.
The word sleek is unrelated to size, it refers to having an elegant, streamlined shape of design. Removing the 3.5mm jack does allow for a more sleek design.
This is what I'm talking about. I don't really use my phone to play music that much (although it is definitely a non-zero amount). The dealbreaker for me is that they've made a device that doesn't lay flat without a case. Although, since it has that ugly bump on the back, it's not like I'd want to have the phone outside a case anyway.
Actually, it's not really about appearances for me. It's just that it wouldn't sit flat. Like a table with 1 leg that's an inch longer than the others at a shitty diner.
Apple permanently lost their "sleek" cred when they introduced the camera bump on iPhone 6. No way in hell Steve Jobs would have released that monstrosity.
It's only smart on one hand (for the reasons you mention). On the other hand users will be pissed off at losing the convenience (yes, convenience) of plug and play headphones, along with the many other reasons why wired > wireless.
It may be a smart move in the end, but it's not obviously so at this point.
