I agree that the Seinfeld hack (aka, "don't break the chain") can be incredibly powerful -- but only once you have a long chain to not break. So there's a catch-22 until then -- you can sometimes keep failing again and again indefinitely, never building up the motivating chain. And that problem repeats every time the chain breaks. So you're always in a precarious situation where one bad day can precipitate many more bad days, where you go down a slippery slope of "one more day won't hurt; I'll get a new chain started tomorrow".
(Extreme bias warning) With Beeminder you can commit to maintaining a certain average, like 3 posts/commits/pages/whatever per week. So it's not all-or-nothing like the Seinfeld hack. You can build up a safety buffer and then take some time off, without the danger that that will lead you down a slippery slope of sloth. With Beeminder's yellow brick road you've precommitted to not let your overall average dip too far.
If the rate you want to maintain is exactly 7 per week -- 6.9 is unacceptable -- and if you can sustain that long term, then "don't break the chain" is probably perfect. For everything else, there's Beeminder!