Your write test is flawed.
Flaw 1: You use /dev/urandom as a data source. Data generation from /dev/urandom is heavily affected by CPU usage AND by available entropy -- though it doesn't block, its speed does vary drastically.
Flaw 2: You only run the test ONCE. This means that issues from flaw 1 are totally visible rather than being averaged out over a large number of tests. You should do the test 100's of times and take the average over them.
Flaw 3: Implementation of the ext3 filesystem tend to hide the effects of disk latency. There are caches and journals that you haven't accounted for. In order to get the ACTUAL time that it takes to write to the ext3 filesystem, you need to follow the write test by a synchronization, which will *actually* write the data to the disk (i.e., it will BLOCK until the write is actually completed). Unfortunately though, this test will also synchronize OTHER write operations that are buffered, which will further skew your results. What you REALLY need to do is perform the tests on a completely empty partition. Should be starting sync, begin time, test write, finishing sync, finishing time. Elapsed time = finishing time - begin time.
In other words, I'm sorry, but your conclusions are not correct. What I *very strongly* suspect, is that if you do your tests correctly, you will find that the performance of swap-on-ext3 will actually be *lower* than swap-on-partition due to the extra overhead of the ext3 filesystem.