My counterpoint is that it's not actually the idea that's interesting, it's the fact that they've convinced lots of people to use it, and have built a system powerful enough to support that scale.
I do think that Twitter's biggest asset are the network effects that it currently enjoys, but I don't think that it would be trivial to recreate what they've done in order to create a Twitter competitor. It's not insurmountable, but it's not trivial either.
The original comment was clearly meant to trivialize the engineering. "One guy can do it in a weekend" is hyperbole, it's something you say when you're trying to communicate that anyone can do something in a relatively short amount of time. If there are a bunch of downvotes I would assume they're more for the hyperbole than people actually disagreeing with whether or not one weekend is enough time to write "non-scaling Twitter", which isn't specific enough for anyone to argue about how long it would take to do.
I fail to see where I am dismissing the accomplishments of the Twitter engineers in pointing out that creating, what is essentially, a RSS feed with a 140 character limit over a weekend would be difficult.
I believe you are complaining over something no one has stated.