How did you determine that it might be number of units and not revenue?

A month or so before me going to look for it, there were 2 games released, one with a pricetag of ~$20 and the other with a pricetag of ~$10. The $20 one was higher in the front page best selling list, but lower in the catalog one compared to the $10 one.
I may remember the numbers wrong, tell me if you want me to go look for said post.

If it's not too difficult, I'd appreciate it. I might try to set up a similar experiment.

Here. Data is (obviously) out of date now, but it was a lovely case of games released quite close, with a big price difference, and their position in the catalog been relevant.

Thanks.
BTW, the front page list is not called "bestselling", just "popular".

Thanks for your explanations, mrkgnao and JMich!

But as I've guessed, no (more official) explanation from any of the blues.

Thank you for the kind words and the bump.
BTW, it is sort of stickied in the Community Stickies Compendium 4.0 thread.

ANNOUNCEMENT:
Version 6.7.0 has been released with the following features:

* Changed the "Filters" and "Order" drop-down menus to be persistent across sessions (i.e. selections are remembered from one visit to another)
* Added "Mac OS X 10.10.2 or newer" to the list of searchable operating systems

Oh great, that's useful!
It was a pain to select the same filters every time during a promo.
Maybe in a far future you could even add custom "profiles"?

That's the next planned feature. Assuming that by "custom profiles" you mean the ability to save the current state (checkboxes, filters, options, etc.) under a name, and later reload it from one of such named profiles.

I need to travel abroad in about a week, so I'm not sure when this will be ready, probably some time in February.

Yes, exactly that!
Great as usual mrkgnao.
And good trip\holiday in advance.

NOOOOOO!!!
I was so looking forward to version 6.6.6! Now what am I supposed to do with all these chickens?! I can't very well sacrifice them on my laptop keyboard to celebrate version 6.7.0, now can I?! I hope you're happy...

...On the other hand, new features are always nice. :)

"And afterward mrkgnao went in, and told HunchBluntley, Thus saith the LADY MaGog of Canada, Let my chickens go, that they may hold a feast unto me in the wilderness."

I just downloaded the JSON format of the MaGog database, and my JSON parser complained when processing it.
From the Quake II game, in the fields "reg_price_full" and "reg_price_curr", I find no data for the "DE" country (Germany).
I am not versed in GoG or MaGog enough to find out why this happens, but my JSON parser expects some value there, and I suppose that the JSON specs say so. I have not checked if other games have this problem.