How can we know how many people buy it just for DVD.I'm sure they are minority

Best selling games still hardcore.

We have 0 proof that people buy it for DVD

Yep, thinking ~115M-120M, myself.

@ OP

Personally, I don't see how people could think the PS4 can't make it to 100M.  Ever since the market grew with the PS1, no market leader has failed to make it to 100M+. The PS4 has also made it to 20M+ without a single PS big hitter.  No GT.  No GOW.  No Uncharted. No (possible) TLOU sequel.  Not to mention all the great new IPs Sony always launches each gen.  We got 2 just around the corner.

And it's done it without a WW price cut.  We still have a cut to $349 this year.  It could possibly be to $299, but if not, then it will be at $299 next year.  Then we have the PS4 Slim, which will come with either the $299 price cut or a $199/$249 one.  Speaking of a $199 price, sales should explode at that point, as long as it doesn't happen WAY late in the gen.  And considering Sony went with off the shelves parts, as well as a memory type that will still be falling in price, I wouldn't be too surprised if they are able to get it down to $99-$129 a year or so before they take it off of shelves.

Even if the gen is cut short by competitors, it is likely that Sony will keep the PS4 going and release PS5 a year, maybe even 2 after the competitor. And unless its a groundbreaking console, the competitors will not be able to topple PS4 sales in Europe and PS dominant countries at that time.

Very true.  We see with the US and UK numbers that the 360 is still selling SW decently, while I'm sure the PS3 is selling decent SW everywhere else.  At least for how old they are.  Meaning many haven't transitioned, yet.  Of course, this happens EVERY gen, which makes me wonder why some seem so surprised by it.  By the end of this year, most games are going to be announced for current gen only, which coupled with price cuts to the consoles, many more will have a reason to switch over.

The basic reasoning behind it is the assumption of a greatly changed electronic entertainment industry since the start of last gen. This includes:

- Shorter hardware cycles (see smartphones, televisions)

- People willing to pay more(hence more early adopters -> frontloaded gen)

- Move away from dedicated devices(move to converged devices)

- Japan not giving a fuck

- casual's complete abandonment thanks to mobile

Stuff like that and some wishful thinking. Of course these are just assumptions based on observations outside the console industry and could be completely wrong.

If you go by these assumptions, the PS4 having a great first year means absolutely nothing and rather seems to confirm frontloaded behavior. So yeah, it's actually really easy to belive PS4 will not reach 100m with the right mindset^^

No Nintendo handheld has sold worse than its predecessor either, look at the 3DS numbers.

I'm still not sold on the PS4 selling more than the Wii, this gen will be a lot shorter and price reductions won't have the same impact on a product that released for a 600$ retail price versus one that released at 400$; the great changes might come at around the 250$ mark in most cases but in the PS4's case; that might be a little too late, developing markets are not the same cushion any longer, they are following the trends of mature markets and moving towards more convenience gaming and fringe titles for more casual customers (Buzz, Singstar, Rock Band etc.) practically don't exist on the PS4 (or One) and those that do are not doing so hot.
Look at the PS3 as well; it is moving super slow compared to the PS2 in these markets and in the twilight of its life, at this rate it'll be lucky to sell 25 million after the PS4 released where the PS2 sold in excess of 50 million.

Of course; the PS2 was market leader and sold a lot more but there is no denying that developing markets account for a lot less cumulative sales; it's not like they're buying 360's or Wii's either...
The market has changed and the fast-paced consumer electronics market will be harsher to static devices such as the PS4, One and Wii U than it ever was to the Wii, PS3 and 360.
In the middle of the 7th gen, there was a splintering of the gaming industry and market and several forms of gaming took of in popularity, this is bound to hurt traditional devices in some way and I believe it is (again; look at the 3DS, not to mention the poor Vita).

Wii wasn't front loaded, it took 5 years for sales to go low. for comparison, wii sold more in 2010 than ps4 in 2014.

Ps2 is 50 millions over 100m do you think 50 millions buy a console for DVD or few casual games

Let's talk about ps3,ps3 sold 85 millions according to vgchartz ,ps3 dosn't have a lot of succesfull casuals games ,ps4 only 15 millions more to top 100 millions it's not that difficut to do that.

That won't happen unless they want to go bankrupt. 10 years is 4 years too long.