No they aren't. new line sets aren't made any thicker then line sets made 20 years ago.
The copper in the evap coil is thinner then what it was 20 years ago.
I think he may have meant larger diameter. Either way an existing line set may be just fine if cleaned properly. I like to change them if they are easily changed like others have stated but cleaning works if done properly.
Amana units with a model number begining with G are relabeled Goodman.
Amana units with a model number beginning with A are true Amamna and not the same as Goodmans.
Getting a Trane or Carrier, doesn't mean it will be installed right. There are plenty of threads about bad installs for Trane and Carrier equipment. It just means those people paid more for the brand name, and still have a crappy system.