I love my laptop and would be lost without it... but my desktop is still my preferred means of computing. With a 24" monitor (the only reason I don't get a larger one is because my desk's hutch can't accommodate that) I get more screen real estate, having a full-size keyboard is helpful when working in SSH on my servers, and the upgradeability of the desktop is important for me as a gamer. Another factor to consider is cost: for two equivalent-spec systems, the laptop will always cost more than the desktop.
As far as the larger monitor and keyboard argument goes though, you can always get said peripherals and hook them up to a laptop at a desk, providing you with a desktop experience from laptop hardware. Then, when you're on the move, just unplug the laptop and take off.
With a laptop, once it starts showing its age hardware-wise, you pretty much have to start considering the purchase of a new laptop... you can give it a small boost by installing an SSD or some extra RAM, but that's about as far as you can take it. With a desktop, you can add multiple hard drives, the RAM upgrade path is usually much higher, you can add the latest optical drive (such as a blu-ray burner), and even upgrade the video... all piecemeal rather than buying a new computer. You can even upgrade the processor to a limited degree (unless you bought in at the end of a generation and the next gen uses a different socket).
Of course the entire upgrade argument hinges on how comfortable you are building/upgrading your system. If you're the sort of person who prefers to just buy your computer, unpack it, plug it in and go, upgrades incur the additional overhead of consulting with tech-savvy friends or a professional to determine your upgrade path, and paying someone else to install it for you.
TL;DR: your mileage may vary; the only two firm arguments for desktop are upgradeability (if you're into that) and price/performance ratio.