Yes, I recently bought a 13" MBP (Retina) for £850 despite the fact I was quite willing to spend up to 2k on a laptop.
Like you, I have a decent desktop, so I had no interest in getting a laptop for gaming, but just to have a system for when I have to be away from home (and so, my desktop). I ended up deciding on a MBP after spending a fair amount of time researching, and these are pretty much the key points:
- While in a desktop I pretty much fully agree with "better spec means better computer" the same is not true when it comes to laptops. If you look at the high end of the market, laptops with 970/980Ms, they all suffer similar issues derived from the simple fact that high energy, high heat producing components and the laptop form factor do not mix well. It is incredibly difficult to combine high specs and a laptop that has adequate cooling, low noise and no throttling and they haven't managed it yet even at the upper end of the market. Of course, there's a genuine market for people who need/want serious gaming rigs and portability, so they sell quite well anyway.
- Linked in with the previous point, you won't find higher spec laptops with as good a battery life as a MBP. Putting a dedicated GPU in a laptop kills battery life, even when you're not running 3D applications, and the only reason Apple have got around this in their higher end 15" MBP with the 750M is by having it switch to the on-board graphics when it isn't needed.
- If you love the design/construction of the MBP (in terms of the unibody design) you won't find many higher spec'd laptops opting to go down a similar path because it's absolutely terrible for heat dissipation.
- MBPs pretty much have the nicest keyboards and most accurate trackpads around. It seems a lot of other laptop manufacturers don't pay much attention to these two (track pads in particular) even at the high end of the market.
- The display is obviously fantastic, but you can also get 3k/4k (better) displays many Windows laptops. The difference is, scaling doesn't suck in OSX anywhere near as much as it does in Win8. Also, 3k/4k is a battery drainer and, frankly, pointless in 13"/15" laptops. One of my 27" monitors runs at 2560x1440 and at this PPI you're already pretty much beyond what the eye is capable of detecting, the 13" MBP (Retina) has a higher resolution of 2560x1600, so an even higher PPI and anything beyond this on a 13"/15" laptop is just a gimmick and a battery drainer.
- OSX is partially based on Linux, so is better optimised and will run better spec for spec than Win7/8 which has obvious benefits on a laptop.
Personally, I ended up going with the MBP because it just seems to perfectly balance design, battery life, build quality and component choice (such as the PCIe storage) to make an excellent (non-gaming) laptop. I also think that if you get the base spec model, combined with the student discount, it's not 'overpriced'. If you upgrade the RAM to 16GB, or the i5 proc to an i7, PCIe storage from 128GB to 256GB or 512GB (you can actually get 1TB as well) you do pay a premium for it (for not necessarily much, if any, real-world benefit) and it starts to become fairly expensive.