If you think that the number of viruses that avast detects is too
small, keep on mind this: if two or more viruses are created with the
same virus generator, they have the same name, because they are very
similar. One of these "families" can contain hundreds of viruses. So
avast detects many more viruses, but many of them have the same name.
Some other antiviral companies count and name the viruses different
way to show to users amazing number, but it´s nothing more than
advertising gimmick.