If the optical drive is an issue, get the 13" MBP. It's still a fantastic machine. Even the 13" Pro is lighter and thinner than a lot of 13" PCs.
As for why switch, well, it's really a personal decision. If think about it in it's most basic form, a computer, any computer, is just a tool. Both will let you surf, chat and write equally well.
The benefits of both platforms are well known. With a PC, you get more spec for less money. The computing experience is passable for most, although there are some design flaws in both hardware and software. PC hardware is quite often made of plastic that feels cheaply constructed. It feels that way when you use it too. Various parts of the machine creak, squeak and flex during use. In all honesty, it feels cheap because it is cheap (both in quality and cost). This doesn't even count the aesthetics (which are definitely subjective) of the machine with vents, ports, lights and stickers all over the machine. On the software side, Microsoft writes Windows for the broadest common spec, leaving the OEM's (who are hardware people, not software people) to fill in some of the gaps with their own. However, with so many manufacturers, you are almost guaranteed to be able to configure your machine in any configuration if you don't care who the manufacturer is.
With a Mac, you get a much more unified experience at the expense of options, technology and specifications. There are no Macs shipping with Blu-Ray drives or USB 3.0. If you want a 14 or 16" screen, you're out of luck. If you want a mid-size tower, you're out of luck, much to the chagrin of thousands of users. Apple provides you with their set of options and if you want something different, you'd better be willing to make some compromises or find a different vendor. Even the limited options come with a higher price tag than a similar upgrade would cost from a PC vendor. What you do get from Apple is a solidly built machine where the hardware and software truly are made for each other. None of the machines, including the polycarbonate MacBook or the MacBook Air feel cheap in the hands. Try applying a little pressure to the super thin screen of the Air and you'll see that there's actually very little flex. While Apple computers might not be as high spec, or be updated as regularly, they sweat the details (such as the depth of the thumb scoop on the portables). With Apple, you pay for the detail and the deep integration of hardware and software. For some, it's worth every penny; for others it's not.
