Firewalls are available in different tiers depending on the features and capabilities needed by the user/organization.
1 - The most basic level is for home or very small business users which provides port address translation, basic NAT, a single WAN poort, limited network ports, and often wireless.
2 - Small business / small enterprise usually has simple to semi-powerful GUIs, 1-2 wan ports, VPN functionality (site to site and client to site), flexible NAT/PAT configurations, and many have add on features such as anti-spam, anti-virus, IPS, and web content filtering (usually for a monthly fee). Often wireless is an option and there may be high availability/load balancing features available for the higher end models.
3 - Larger Enterprise models will have ports that you can designate at will as internal/external, VPN functionality, powerful GUIs, high speed backplanes, more powerful processors and larger quantities of RAM, high availability/load balancing support, many of the add on features mentioned in the the previous tier.
If you look at firewalls from a larger enterprise perspective, you need high availability which means multiple firewalls in high availability or clustering mode supporting multiple ISP connections. Not only does the hardware add up but your annual maintenance is a pretty penny.