Zeewolf: Well, it's just that these games can be found in pretty much every regular game store you can think of (often in bargain bins), and pretty much every digital distribution site as well. So there's a lot of competition here, including the biggest players in the distribution industry.
Basically, I think that while the addition of these games are great news for most of us who are already fans of GOG, it's not going to be that big of a deal to the rest of the gaming population, because they can already buy them wherever they want. And I suspect they'll - for the most part - get them wherever they're cheapest.
On the first point, finding older games in retail stores is tough for me, I usually would have to buy over the internet, and even then, I hate using the UK postal system for packages, I've had three packages lost in the past two years, very annoying.
Out of interest, what other digital download stores are available in Europe? I know Steam covers most of the world most of the time, but I wasn't aware that there were other big players, I have avoided this sort of thing until GOG came along.
On the second point, you kind of back up my original idea, that the increased variety and extras will retain customers for repeat purchases. They are still going to offer the older more niche titles, but have the bigger ones as well. The best of both worlds.