From my experience I can say that the “old IBM machines were reliable and well constructed” is not true. They were bulky and over time, everything breaks. Especially the heavy stuff as bulky things take so much more wear & tear. The newer machines are much thinner and lighter and still very good. At least the T and X lines. I exclusively buy Thinkpads for my team and have been very happy with them.
The only thing I really miss is the thinklight. Not super useful, but it was just so cool.
Edit: I always buy barely used machines of about 2 years old, this seems to be the most cost effective.