How often do you archive 50GB of Data?

I'm going to guess not that often. So why add the extra weight and expense to your laptop?

Personally, I wish they would drop the optical drives altogether across the line and have them as external options. Even better: how about put it into Time Capsule.

The only time you really need these things is when you are ripping media into your portable library or, as you pointed out, you are trying to archive or backup content/data.