Wikipedia explained that:
The open source vs. closed source (alternatively called proprietary software) debate is sometimes heated.
Making money through traditional methods, such as sale of the use of individual copies and patent royalty payment, is more difficult and sometimes impractical with open source software. Some closed-source advocates see open source software as damaging to the market of commercial software. This complaint is countered by a large number of alternative funding streams such as:
- giving away the software and charging for installation and support (used by many Linux distributions)
- make the software available as open source so that people will be more likely to purchase a related product or service you do sell (e.g. OpenOffice.org vs StarOffice)
- cost avoidance / cost sharing: many developers need a product, so it makes sense to share development costs (this is the genesis of the X Window System and the Apache web server)