As someone who was starting to look at upgrading his phone (5s going strong so far), I know that the lack of headphone jack is going to make me sit right back down and wait on the purchase.
I bet you said the same about PS2 ports, floppy drives and the recently defunct CDROM drives too.
Since you asked (assuming you mean the removal of those technologies):
1) PS2 ports were fine for the Keyboard and Mouse, but honestly USB was a great technology to replace both those and the Serial Parallel ports (and honestly one I looked forward to since it simplified cabling and wiring). The removal of the PS2 ports happened gradually though, after USB had a chance to appear. There were also more options available at the time in terms of Windows computers. Hardly a comparable comparison.
2) Floppy Drives were a bane. I certainly picked up a USB version for the rare times when I needed one, but it wasn't something that affected my buying choices.
3) The recently "defunct" CDROM drives? Honestly, I can't remember the last time I bought a CDROM drive, probably ~1999. Since then its been CDR/DVD/Combo drives all the way. If you're referring to the removal of generic Disc drives, then I'd also point out that this wasn't something that happened all at once. My laptop from 6 years ago came with a disc drive. It also supported USB. The transition to flash drives and everywhere internet access is what drove and allowed the removal to not affect most people. External optical drives also allowed those who wanted/needed one to keep using one.
Yes, assuming Apple does away with the headphone jack in favor of a Lightning connector, I am sure there will be adapters available, however the main reason for the previous changes you listed were because the technologies listed (PS2, Floppy, CDROM) had been obsoleted by existing newer technologies.
In this case, Lightning headphones are a recent niche innovation, solely related to iOS portable devices, and the change will impact the majority of people who use those devices.
Further while the change may certainly make the iPhone slightly thinner (is anyone really calling it fat?), the change also means Apple gets to cut the jack, the DAC and all the ansillary circuitry from the new iPhone, which I'm sure help drive costs down a little bit.
Will it ultimately allow them to make the phone thinner, more waterproof, and allow them to deploy a full wrap-around screen (as some analysts think)? Maybe, and I can understand why it might be good for Apple to implement this technology NOW to help get the market ready for those changes, but I'm less confident that adding a new adapter is going to be that great for the consumer (but for Apple, yeah sure, great move).
Will that alone mean I don't get a new iPhone?
Honestly, dunno. I was on the fence as it was. The additional space and speed would be nice, but as Apple's iPhone sales have shown, existing phone technologies are sufficient for lots of people to not need the latest and greatest as fast as they used to (similar to how computer technologies have advanced to the point that most people don't need to refresh them every 2 years).
If I have to add more costs and changes to the phone purchase (new headphones? adapters of uncertain longevity?) I may take my usual stance on any of Apple's (or any companies) new "innovations".
Wait a revision or two for them to iron out some of the small problems that will almost inevitably crop up. By that time either the market will embrace the change, bringing with it more choice in headphones and adapters at lots of quality and price points and with the added design experience from lots of real world trials (I'm looking at you original iPhone headphone jack), or the market will reject the idea and we'll see the re-introduction of the headphone jack to the next iPhone model.
Honestly I doubt they will revert the decision (if it has even been made, since no one knows apple's plans but apple), but it seems so silly that at the point that everyone (including airlines) have adopted the headphone form factor, Apple has decided to remove it from their lineup.
tl;dr I need lunch :)