1 Million in the first day... not a very good result in my opinion.
Think of it: on the first day, many peope downloaded Applications because they knew, there was the AppStore coming and were eagerly awaiting it and of course downloading (not necessarily buying) something. But that was the first day and now, it's the turn for all other people.
As the Update is available via SoftwareUpdate, it takes a week (which is the default in SystemPreferences) until everybody at least sees the update. Then, when the installation is finally done (which many users choose to delay for several weeks), the only thing, the user may notice is the new icon in the dock. As the dock usually is packed full with other apps, most users will not notice for some more weeks, if ever. I mean, I just looked at my dock in detail as a test and found out that there still was iPhoto. I never used it on this computer but I forgot to remove it from the dock, so it was still there after 8 months.
And when people finally click on the AppStore icon, they find a store for strange things. There is no explanation what this is, people don't know what this thing is for. It looks like unwanted advertisement.
So, after one million downloads on day one, I do not expect an impressive increase in daily downloads. Maybe I'm wrong, who knows. Just my thoughts.