Simple answer: Yes. With delta timing you don't actually know what the hell your end-user will get to see. Not knowing what you're presenting means you've failed as a designer, regardless of how technically superior that fancy-pants timing code makes you feel inside your own head.
And, of course, if you're honest about your required specs then slowdown won't be an issue.
I think there's an insult there somewhere, but I'm not offended. I think you are wrong.
The problem is with "And, of course, if you're honest about your required specs then slowdown won't be an issue." -- firstly, many users don't know their own specs. Secondly, many things can happen that makes a pc run out-of-spec.
Therefore I will just have to try my best. BTW: "regardless of how technically superior that fancy-pants timing code makes you feel inside your own head." -- I don't understand your problem. This isn't about how clever I feel, I am not one of those people. This is about how I can deliver the most similar experience on the widest amount of machines.
For "Slowing down" affectionados, please be aware this alienates you from every realtime multiplayer game there is. It's simply no solution at all for games.
I understand where a lot of you are coming from - I'm likely a lot older than the majority of you and have played those old games, but time moves on... it doesn't slow down ;)