Microsoft’s standard support policies dictate that mainstream support will provide free fixes for security and bugs for the life of the product. Mainstream support usually last 5 years after which the product would enter a period known as “extended support.”
“Extended Support” is only provided to customers who have signed support contracts with Microsoft. While Microsoft will continue to provide security fixes for a product for free, any bug fixes or non-security hot fixes will require extended support contracts.
Naturally, Microsoft wants few people on these types of support contracts as possible, promoting that customers should consider upgrading. Upgrading, however, isn’t always an option so getting extended support is a good way to cover the needs of an enterprise. SMB markets won’t be affected too much by this because they don’t typically do a lot of heavy customization and integration work like enterprises. For what it’s worth, Windows XP and Office 2003 have had a great run!