No, if you buy it while its on sale, then as soon as the full price drops to what you paid during the sale, then you can download the new version for free. Take the most recent update for example. It was $10 until three days ago, when the price dropped to $5. Since I purchased it for $5 months ago, I had to either wait until the price dropped, or pay the full price. Feyada is usually pretty reasonably quick about lowering the price to allow those who purchased on sale to get the new version, for this particular update, it was only 13 days.