I think download sites initially helped software companies who offered evaluation versions a good channel to sell more software. Now they are irrelevant. As far as how freeware is impacting software sales, I think people are learning you get what you pay for, and little in life is truly "free".
Regarding office suites I personally have enjoyed using Wordperfect including the Corel suite version, followed by Lotus Smartsuite, followed with regret by MS Office.. then migrated to Openoffice/NeoOffice (Mac) to escape MS. Now I use the fork of Oo that is Libreoffice on Linux.
Using PCLinuxOS (as with other Linux Distros) means the availability of included open source software to perform the functions I require.
If you want information on proprietary software.. CAD/CAM, specific industry software for example, then I can't help you in that area.
How about using the Cloud? Do you need to cover that aspect of the use of programs?
Bellow is description of business software
Business software is generally any software program that helps a business increase productivity or measure their productivity. The term covers a large variation of uses within the business environment, and can be categorized by using a small, medium and large matrix:
The small business market generally consists of home accounting software, and office suites such as Microsoft Office and OpenOffice.org.
The medium size, or SME, has a broader range of software applications, ranging from accounting, groupware, customer relationship management, human resources software, outsourcing relationship management, loan origination software, shopping cart software, field service software, and other productivity enhancing applications.
The last segment covers enterprise level software applications, such as those in the fields of enterprise resource planning, enterprise content management (ECM), business process management (BPM) and product lifecycle management. These applications are extensive in scope, and often come with modules that either add native functions, or incorporate the functionality of third-party software programs.