Reading your comment I was under the impression they stole someone's design. Looking at your links, there is no resemblance between the two save the dinosaur.
Hmm. I get the impression that this was written by a someone who's main activity is designing.
I look at it this way. Form and function go hand in hand. The reason Tumblr is successful is because it's well designed AND it works. Where as Posterous, well, the design just isn't as pretty. It still works though...
If I had to choose though, I'd rather make something that works than something that just looks pretty.