Lenovo didn't have enough influence over their platform to shove software keys down the market's throat and get any 3rd party software adopt them in a useful manner. If you're developing software for Windows, that particular version of the Thinkpad is a vanishingly small portion of your target market. With Mac software and the MBP, it's a substantial one.

Apple's positioning here is fairly unique. They can add this feature and expect a significant number of developers to actually implement it.

Software keys on their own to just control the computer's built-in functions don't strike me as particularly useful. The strength in this is like Steve Jobs' original pitch with the iPhone's touchscreen versus a fixed hardware keyboard. It can adapt to new uses and functionality as needed.