It is a guess, but a guess based off of history and the power of the PS brand. 

PS easily outsold the N64 + Saturn

PS2 easily outsold the DC + GC + XB

Wii was an oddball and the XB 360 was going against a $500 ($600 for the good one) console with a year head start, yet still got outsold. 

Wii U is no Wii & XB is dead outside of America.

PS4 will take them both combined with little issue.

I'll agree that at this point nothing is guaranteed but I'd say my thoughts are logical.

Lol what PS4 just started and is already treading water compared to Wii. To match the wii you need to show something that completely changes the way "wii" look at games

Xbox one has a huge price cut: PS4 still ahead
Wii U has a huge selling game: PS4 still ahead.
PS4 has... nothing and it still ahead.

You sound like me from a few years back. Sad really :(

The difference between the Wii and PS4 is the grandmothers who bowled last gen either went crippled or died 3 years after it launched. The PS4 audience however will still be alive and buying games when this gen is over..

The Wii was doing 250k-300k a week this time in 2007.

PS4 is back to PS3 sales by last year.

I can't wait to come back to these threads in 6 - 7 years (if I remember) and read up on all these predictions of over 100m sales for the PS4 and when i see the 70-80 million number, I am going to laugh at you.

Let me put things into perspective. The Wii sold 100m world wide yes? People are saying the PS4 will be 100m+ worldwide because it is selling so well but if you look at the Wii, it was selling 2-3 times (sometimes even more than that) by this time than what the PS4 was and it did this for several years. And the Wii sold more than the PS4 did by this time. The numbers pretty much never made it below 150k a week until around summer/fall 3 years later and then it was STILL over 100k per week. Something that the PS4 is not doing right now and it probably won't do... ever. The PS4 sale surge is over. You are going to probably continue to get these numbers with them slowly declining over all over time with spikes here and there but it will NEVER get to 100m. The only way I can see it doing that is if they keep it going for an extra 3 or 4 years into the next generation and I doubt you will see them doing that otherwise it will be Sony being left behind next gen instead of Nintendo.

Just so you know, by February 2012, the Wii was still selling more than what the PS4 is now. If the Wii was crippled or died after 3 years of it's launch, what do you call the PS4 who is selling worse than a crippled or dying system 2 years after it was crippled or died?

Wii was three times as much no way ps4 wont reach ps3 numbers

Finally a smart poster.  I second this, and this will be my last responce in any such topic.

The ps4 will still out sell