The Ubuntu installer has always been based on the Debian installer ("d-i"), and given our heritage as a distribution it makes a lot of sense to take that route. While the version you see on Ubuntu desktop CDs has a customised frontend, much of the backend code is shared with d-i, and this is particularly so for the partitioner - partitioning code is sufficiently delicate that we have no desire to maintain two entirely separate versions of it!
d-i's partitioner is called partman, and it's been used in all versions of Debian since 2004 or so, and in all versions of Ubuntu. We have contributed extensively to d-i over the years, and I'm one of the primary developers of partman among other things. (I guess it isn't fashionable to regard Debian as an upstream or something, but in this case it certainly is.) Like many partitioners, partman uses libparted, one of whose maintainers indeed works for Red Hat.
If you select "Specify partitions manually (advanced)" in the current Ubuntu graphical partitioner, you'll get something that's essentially a graphical rendering of partman's dialogs (though there are a couple of features missing). I wrote that graphical frontend for Ubuntu, and it has not been changed much in 10.10. The big changes are in the automatic partitioner, whose job it is to supply a small number of clear common-case options; Michael Forrest gave us a new design for that, and Evan Dandrea implemented it. Those changes, the ones mentioned in the main article, can and should be credited to Ubuntu.