Well, the Thinkpads I'm familiar with normally range in the ~$2k mark.
I believe that's usually with a discrete video card though.
Are you opposed to buying used, or is new a must? Used can get you a fairly good laptop for much cheaper, although warranty length is hit or miss depending on the age of the model. For a comparison, when I bought my T42 15" laptop a few years ago, it cost close to $1800. When that finally died, I got a comparable T60 15" used for $600.If you don't mind used, I'm sure you can pick up a nice T60/61 for around $800 or so.
If you want to go the new route though, that limits your choices somewhat. Is an IPS/Flexview LCD panel important to you?
Also, with a 15", I believe tablets are out, so if you want/need tablet functionality, you'd need to scale down a bit or splurge for the behemoth with a built-in Wacom.
The two you linked have differing screen sizes, 14.1" and 15.4" as well as being from different product lines.
Lenovo Thinkpads
See which series suits your needs best and look around for models based on what you find.
There are some slight differences in build quality as well. Unfortunately, I do not have experience with all of them, but I do recall that the "R" series is not as durable as the "T" series since the "R" was more consumer oriented and the "T" was more business oriented. Of course now they've decided to make like 6 different product lines, so who knows.
Edit:
I freaking hate this board's linking system. Takes like 5 tries to ever get a link to display properly. Good riddance whenever we finally switch to vB - a proper forum software.