Might be the OS X version but my work 2012 MBP, 10.8.4, has 4 GB RAM and a 500GB HDD. With a text editor, an email client, a couple of terminals, a couple of chrome tabs and an IDE open, the RAM gets loaded and the swap starts to trash. I get huge slowdowns all the time.

With my own MBPr (10.8.4), I have 8GB and never get into similar cases. And having a SSD instead of the HDD, I don't fear nearly as much the day I'll hit the swap.

The OS itself takes over 1.2GB of RAM, add to that ~1GB for the IDE (IntelliJ), ~1 GB for Chrome tabs, that's already > 3GB. Add the terminals, email client, various other processes and daemons... 4 GB is not much.