When was the last time you visited a Web site where the second-level domain was a single letter, like “a.com”?
Considering that shorter is sweeter with domain names, I was surprised that I could not recall visiting any such site.
A little searching yielded the reason: In December 1993, the Internet’s governing organization reserved all second-level domains comprising one character or digit. Excepted were six existing domains (i.net, q.com, q.net, x.com, x.org, and z.com).
In November 2005, the possibility of reversing the policy was raised. This MSNBC article from the time explains why the single-letter domains were restricted in the first place:
Single-letter names under “.com,” “.net” and “.org” were set aside in 1993 as engineers grew concerned about their ability to meet the expected explosion in demand for domain names. They weren’t sure then whether a single database of names could hold millions — more than 40 million in the case of “.com” today....
One idea was to create a mechanism for splitting a single database into 26 — one corresponding to each letter. So instead of storing the domain name for The Associated Press under “.org,” it would go under “a.org.” In other words, “ap.org” would become “ap.a.org.”
Now, engineers have concluded that won’t be necessary. They have seen the address database grow to hold millions of names without trouble, so they are now willing to let go of the single-letter names they had reserved.
That said, I found no indication that the policy was later changed.
So perhaps the way to look at things is: The original reason there are so few single-letter domain names was technical. When the technical problem went away, it left the political problem of how to allocate the new names, a problem that apparently is still pending a solution.