Lenovo laptops, like every other brand you have ever heard of, is made by an ODM. Mass market machines are made to fit a certain price point and upgradability goes out when trying to met specific price points.
Limit your future laptop choices to custom builders and you will have that option within limits. Specialty shops like WidowPC.com / FalconNorthwest / Alienware / Voodoo PCwill custom build these things though a top end rig might cost you $4500. For about 2/3 of that price, you can cut out the middle man and go to an ODM supplier such as www.pro-star.com who is a US supplier for Clevo who is the most "cutting edge" of all the ODM's. If you are wondering why all the laptops at all of those specialty shops look the same, it's cause they don't actually build anything ... all they really add is the case paint and a logo. All their models are Clevo machines.