I just found out that Canonical (the Company behind Ubuntu) did a nice paper on rsyslog, which also explains why Ubuntu chooses rsyslog as its default syslogd.
It is interesting to see that the paper is well-written and well-researched, but rsyslog has also evolved while the paper has been written. So in fact, it offers even more features than described in the paper.
And, obviously, I am glad to see Ubuntu move to rsyslog as well.