The only benefits HTC has are:
1.) HTC is only better in it's "build quality" and "appearance". But once you shove it in a case, build quality and appearance becomes irrelevant.
2.) Front stereo speakers.
Galaxy S4 crushes HTC One in everything else.
Not sure why anyone would get the HTC One over the Galaxy S4.
The case thing is an assumption, unless you are talking about certain individuals. Not everyone uses cases. I don't, as it doesn't guarantee protection of the screen from shattering, unless you want to add a big bulky case. Which negates some of the lower weight (which I see a lot of people mentioning) if you are doing so with the S4.
Also, the S4 beats One in terms of daytime shooting, but not at night. I haven't seen video/microphone comparison, though.
Internal specs of CPU/Memory for S4 might be higher, but in terms of actual usage is it faster? Like noticeably faster in terms of running apps? If not, I wouldn't say it "crushes" the HTC One. I haven't noticed any lag on my One. I think quad core with Jellybean or higher (Project Butter is what made the difference) has made Android pretty smooth on any quad core Android smartphone. Talking about how good the S4 is specs wise - unless you are running some high end apps - is like comparing the i5 to the i7 or 8GB DDR3 to 16GB DDR3 if all you are doing on a desktop is web browsing. Is 1.9 GHz vs 1.7 GHz making a huge difference when you probably aren't truly multitasking video apps and games? I don't know, maybe that's just me.
The S4 does have a bigger screen, but get this: I don't actually want a bigger screen. The One is actually pushing it for me at 4.7", as any higher and it's a stretch (literally) to use it one-handed. I don't want a phablet. I think 4.3 - 4.5" is probably ideal, and 4.7" is acceptable, but I don't want 5" or higher. If you like the S4's size, that's fine, but it's not the ideal screen size for me.
If you want the greatest specs, go ahead, get the S4. Personally, I'm not competing to have the best paper specifications. And one feature you did mention - the speakers - is far more important to me than .2 GHz advantage or eye scrolling or whatever else is unique to the Galaxy S4. If that's what matters to you, that's fine. I understand chasing specs. But if you are "Not sure why anyone would get the HTC One" you must not be reading any of the reviews comparing the two phones, or reading what people are posting in this thread. There are plenty of reasons to get either phone over the other. Or even the Nexus 4, or Xperia ZL.
I paid $200 with contract for my 32GB HTC One (which included a HTC Media Link HD for the preorder). I'm very happy with it. I'm getting a S4 for my brother when it comes to Verizon, but I doubt I'll regret buying the One even after playing with the S4. Even if you think the S4 is better - and it's certainly a very good phone - it should be obvious that the S4 isn't so substantially better to make it a "no brainer" as someone else said. Personal use cases matter.