A few starting points:
1) VGChartz are notorious for unreliable numbers. They have a somewhat solid foundation but are missing important retailers and used to use NPD numbers (until they stopped releasing them) for course correction. Use rough numbers for trends, not specific values.
2) Like drill_sarge mentioned, Steam doesn't divulge sales numbers. It would be interesting to know how Rage fared on Steam compared to other games and see if the big download size made a difference.
As Argoon1981, the PC release debacle absolutely caused problems. I wouldn't be surprised if there were cancelled pre-orders in territories that got the game later (Europe, etc.) because of it.
Having said that, my personal expectations would be for PC to roughly hold its own against either console. These numbers are problematic. It will be interesting to see if the patch and drivers change this trend for the following weeks.
Claiming the console market is much more important than PC can become a self-fulfilling prophecy: if you constantly advertise in interviews that the PC version will have few, if any, advantages and remove a COOP mode from it then people who would have otherwise bought the game on PC will probably just get it on console instead.
Here's a question: if these numbers continue, will the next DOOM be console-only? I.e., during the first month, the console versions combined have 2 million (accounting for some drop off) and the PC has 0.5 million (doubling the current weekly value to account for the patch, etc.). If you don't think id would skip the PC, regardless of Rage PC numbers, could you explain your reasoning please?
Steam sales are the wildcard obviously, what we know so far is that Rage has been the top seller on Steam in the first
week and that by looking at those lists, there were no other new AAA releases in the same window. Hard to gauge the sales number but I did find this
article. Basically, October 2010 was the third best month for Steam where Fallout: New Vegas had a total (month) sales numbers of 308,000.