It seems to me that Going Postal was more topical than Monstrous Regiment, but perhaps that is because I am closer the industry that is the focus of his scrutiny. The x-files and internet references were also pleasant for me. That and my worship of Anoia at my house make this my favorite of the recent books.
Did you know the reference in the title of Monstrous Regiment? I did not until it was alluded to on a As Time Goes by.
If you want magic, read the Tiffany Aching books. I am quite take with them. This new kind of book was forshadowed by first Reaper Man and then Small Gods. In both he has points and purpose, whereas in the Colour of Magic he seemed only to be telling a tale and the points were incidental.
When Robert Asprin and Piers Anthony grew topical, their series went down hill. I don't know if that is because they let their point matter more than being entertaining, or that their points were simply bitter pills to swallow. The themes that Pratchett has chosen resonate with me without making me uncomfortable at all. Topical fiction especially fails to entertain when the autor either tries to make points that are at the expense of their readers or are completely irrelevant to their readers, unless the author has taken care to be extraordinalily entertaining. Asprin and Anthony seemed to forget how to tell a good story. Pratchett has not forgotten and so far seems to be getting even better.
The other way topical fiction fails is when it is too heavy handed. Like Hawthorne and his symbolism or Hemmingway and his macho terseness both hammering home their points right through the skull of the reader, so much so that others merely in the room as the reader are at risk of injury. Pratchett risked this in both novels you mention, but he had me until the end in both. In monstrous regiment, I had to know what happened next to the very end, and in Going Postal, I found the characters compelling. I loved Killer/Spike. She ranks right up there with Death in my eyes.
By the way, how does one get paragraph breaks into these entries?