Even taking build quality into account the MBP's are still less than stellar values. When I bought my x220 I compared it to the MBP 13 and for the same cpu, gpu, and ram the MBP was several hundred dollars more expensive. Plus the Thinkpad had close to double the battery life of the Mac, a significantly better screen, and was better engineered and built (The MBP 13 has terrible cooling while the x220 always stays very cool). Lenovo also offers next business day on site support for a small price increase that more than negates the Apple Store's support offerings.
Thinkpad are an exception no one is going to argue they arn't well made. But still, they are plasticy. I love the all metal unibody of the mbp and that will never change.
x220 as awesome as it is as a Laptop is kind of ugly too I think it's also well over half an inch thicker than the 13" MBP.
I'm looking forward too see what the new MBP looks like, as it hasn't had a significant redesign in quite a few years.