Although not my first Mac purchase, at the time I bought my 2010 13" MBP, the alternatives in the Windows world were pretty disappointing (I'm an IT consultant and pretty much see and work with everything out there). To my mind a well made portable computer should share many of the same hallmarks of a good camera:
1) Solid Construction:
Frankly, nearly all windows laptops are frankly, poorly made. Cheap materials, assembly/disassembly incredibly difficult. There are some exceptions - the recent Lenovo's are very nice, the new high end HP offerings are nice... My biggest issue is CRAPWARE - the first thing I do with *any* major manufacturer's box is to do a clean install, followed by device drivers - honestly this takes less time than "de-crapifying" whats there.....
2) Battery Life:
A portable computer ought to reliably be used all day, or close to it. Honestly, the only way I've been able to get most Windows laptops to work that way is to change power management to hibernate on Lid close. Carrying a spare battery is in my mind, a must. I've been very pleasantly surprised by the power management of the Mac - I rarely run it into deep sleep (hibernation) even though it is *always* on and with me during my workday.
All current MBP's offer Thunderbolt, a portable interface with PCI-Ex and Displayport capabilities. Although a bit expensive, there are some impressive offerings out there including Storage, Video Capture, Video Processing, and external PCI-Ex cabinets - effectively turning your purchase into an effective Workstation class machine. To my knowledge, only 2 Windows based vendors support TB, Sony and Asus (neither shipping - although this will soon change...)
Frankly, I enjoy running both Win7 and OS X - the operating systems have far more similarities than differences. If you must run Windows apps - a great alternative to Parallels is Oracle's Virtual Box - I have several Virtual Machines on my Mac including Server 2008R2 hosting Active Directory, and Exchange Box and a pair of XP and Win7 machines, I use these to help support customer's issues. All running quite effectively in 8GB I also run bootcamp - natively booting into Windows 7, but rarely use it....