It's not uncommon; Visual Studio's release cycle is around every two years.
To work out the math a bit, say the developer is looking to make 70k a year (which is quite low IMO, especially if you are self employed). If his release cycle is every two years, he needs to make 140k over one version. At $59 for S2, thats around 2400 sold copies over two years. Not a small number for a product that is tailored to such a niche market. Also considering that there comes a point where the purchases trail off, so the developer needs to find a way to sustain an income. Upgrades seem like a very reasonable way to do that.
With S3, if the developer wanted to offer a reasonable way to allow S2 owners to upgrade at a discount, it comes at a loss of income for the next two years. Given that the amount of people who would buy the editor have already bought S2, so the pool of possible purchasers decreases. So it seems like a reasonable balance to allow that discounted upgrade, while increasing the full price to make up for the loss of new purchasers.
To work out the math a bit, say the developer is looking to make 70k a year (which is quite low IMO, especially if you are self employed). If his release cycle is every two years, he needs to make 140k over one version. At $59 for S2, thats around 2400 sold copies over two years. Not a small number for a product that is tailored to such a niche market. Also considering that there comes a point where the purchases trail off, so the developer needs to find a way to sustain an income. Upgrades seem like a very reasonable way to do that.
With S3, if the developer wanted to offer a reasonable way to allow S2 owners to upgrade at a discount, it comes at a loss of income for the next two years. Given that the amount of people who would buy the editor have already bought S2, so the pool of possible purchasers decreases. So it seems like a reasonable balance to allow that discounted upgrade, while increasing the full price to make up for the loss of new purchasers.