The number of possible domain names is 3.17 x 10 to the 34rd power. That's a really big number, so we're not going to run out of domain names anytime soon. Really good marketing names are going more quickly. Knowing that short domain names are in short supply probably further increases their demand.
Pressure is also extreme on domain names that can be found in an English dictionary.
For example, among the 456,976 possible combinations of four letters, less than 25,000 have any meaning. English names are unregistered. The statistics do not matter if you can find the appropriate domain name for your business. But predictions are that there will be 100 million domains registered within 24 months. One of the best ways of capturing a good name for your business is to take two short words, which may or may not have any particular meaning, but which are distinctive.