That should really be the "100 Oldest .com Domains". Before the .com days, the internet had two top-level domains: .ARPA (for ARPANET -- universities and companies) and .MIL (for MILNET -- U.S. military). BBN was BBN.ARPA long before it was BBN.COM (they developed the original internet routing hardware).

Since the old .ARPA domains no longer exist, the oldest domains still in use today would probably be the .MIL domains (e.g., army.mil), which date back to 1983.

Wikipedia has a diagram of what the entire network looked like in 1977: http://en.wikipedia.org/wiki/Arpanet