Steam Profile/Achievments don't accomplish this?
Anyway, reddit Karma is probably just as meaningless as gamerscore, not sure why that's justification.
I get the appeal of having a badge or whatever saying you did something. Just not the arbitrary point value attached. Which is what you were talking about in regards to Steam achievements vs gamerscore.
Your missing my point in the ease of viewing individual achievements for individual games (i.e., nobody will make the effort to do so, therefore nobody will ever see them) vs an overall score being readily apparent at the basic level of viewing one person's profile.
If you click on someone's name in Xbox Live and go to the basic profile page, the Gamerscore is proudly on display right next to the account name. It gives an immediate representation of the person's dedication to achievements.
To get the same idea for a Steam user's dedication, you have to start clicking through menus.
Even just a display of the total number of Steam achievements that have been acquired (disregarding an arbitrary numerical value attached to each individual achievement) proudly displayed next to the name on the Steam profile would be a huge start.
They could easily implement something like this very easily if they wanted to, it's not like Valve is incompetent. I'm sure the way Achievements are handled on Steam right now is on purpose, I just disagree with their vision.
Also, I wasn't using Reddit Karma as a "justification" for an overarching score tied to your account, just merely as an example of the things people are willing to do to raise a numerical value to show other people. It's deeply psychological... and even slightly pathological.