I don't think copying Twitter as a whole is easy nor do I think just anyone can do it. As pointed out, a simple non-scaling version of Twitter could be done by a competent developer in a weekend. I'm a front-end developer and I feel confident I could do it, just not in a weekend.

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.