Actually I'd say the opposite. If I put down $500 once, I have that version. Patches and similar free updates don't sell me another copy or make the company any money. The only way to get more money out of me is to sell another major revision.
In a SaaS model (i.e. subscription method) I can jump ship in 6 months to another product with better products/features/updates and not lose my whole investment. Instead, if I'm paying the company monthly they have a very strong motivation to continue improvement. It basically removes the need for a major/minor release schedule. Just keep paying and you're guaranteed the latest, updated version regardless of what number it's assigned. If I walk away, I'm not out anything so the company is driven to keep me happy - in return they have a regular, predictable income stream that accountants and investors love to see.
Think World of Warcraft...though they do charge for major releases it's about the same cost as a 6 month sub (IIRC). Inbetween they constantly update, patch, monitor, etc. Granted they have FAR more overhead in running the servers the game 'exists' on which justifies their monthly sub.
I still don't like SaaS but I understand the business model. However, I prefer to own "my" things instead of giving some company arbritrary control of whatever they like. Some "fixes" are anything buy.