In theory, you can host an unlimited number of sites and software on a single hosting account, as long as you have enough disk space and CPU time to handle it. The given sample number of sites is more of a recommendation and is directly related to the number of domains your plan allows. For guidance, you can see the "Number of additional domains" column in the detailed characteristics table. If the number of additional domains is 0, then you can use only 1 domain, if it is 10, it means you can use 11 domains (1 main + 10 additional). You can host additional sites or other software on subdomains, which are unlimited for all plans.