Not everyone who buys products on RPGNow/DriveThruRPG accepts emails from those who published the product they purchased.
This is often understandable. Fear of having your email account flooded with updates from many different publishers can account for this – although this can be a good reason to set up a separate email account.
Not getting emails from publishers means that you can miss out on special offers. For example, the recently released Tomes of Alchemy had a special discount sent out to everyone who had purchased a product previously, and agreed to receive emails.
This wasn’t everyone who had purchased of course. Those who hadn’t agreed to accept emails didn’t receive this special discount. Some of those who did took advantage of it. It’s possible that some of those who hadn’t subscribed bought the product at the full price, missing out on a discount.
We often target emails to a certain degree, although finer targeting is going to become less possible as more products are published. Still, at the moment, assuming that you qualify for every email sent out, this only means one email a week. Most won’t be discounted, but some will, with the discounts tending to be for the more expensive products.