For a Macbook Pro, can you join more memory or is that solely for the unyielding drive?

Answer:

You can include more memory. Look in the Users Manual for instructions on how to add/replace RAM.
You probably can.

Needless to read out it would be $$$ and have to be done by a professional
Yes, five minutes... if you don't know what to do, else it's smaller number time.

http://www.ifixit.com/guide/mac/macbook-...

You can select other models, and parts, they have righteous guides :)