The difference is probably still mostly digital copies and like someone here said earlier the only place where it is actually undertracked by a fair amount is probably Europe.  Also your underestimating how many people download free non manditorty DLC since over 1 million people downloaded the 1000 Club DLC for Forza Horizon.

See, that makes sense though :

http://www.vgchartz.com/game/70780/forza-horizon/

Comparative numbers are ~1.74M for FH, so that's pretty far from 100% (which this number would indicate over 100% discounting digital sales).

Now including digital sales : http://www.gamespot.com/articles/29-percent-of-game-sales-digital-purchases-npd/1100-6285488/

You get a number that shows 29% of console games are digital now. This number is probably fairly heavily skewed by the prevalence of small indie/simple titles and PS+/GWG stuff as well. So maybe for AAA games, the number is 20% or less.

So take the 2.4M x 1.20 = 2.8M. So 2.5M of ALL (2.8M?) GT6 players are still both ONLINE *AND* play it actively enough to download DLC (free, update only, whatever)?

I simply don't buy it, that doesn't make sense to me with everything that I know about how not everyone connects their consoles online (a majority do, but substantial numbers still do not, even in 2014!), and further, I know how people tend to discard games after a few months and never play them again.

It's much more likely that

(1)- GT is much more popular in Europe than the US.

and

(2)- VGC tracking in EU is ... poor, to put it kindly.

and that equals :

(3)- GT6 is fairly heavily undertracked!

or multible accounts, downloading the add on
same Thing we got with forza 6 numbers.

not sure, how they Count Downloads
but still a solid figure to see how big (or small) the game is

Well the 1000 Club DLC came out a lot later in Horizon's life cycle then this update for GT6 as a matter of fact it was the last DLC for Horzion and by that time probably less then 50% off the people that owned it where still playing it.  So overall probably over 50% that still played it since the 1000 Club DLC was released downloaded it which is pretty good for a free non manditory DLC.

I agree. I also bet that FH is farily undertracked given what we know. 1.74M sounds low for such a title that would get 1M DLs.

Now there is pure undertracked (estimates of sold-through at retail being too low compared to the true numbers)

and then there is digital undertracking, which basically is true of every title to some degree or another.

With FH I bet the retail tracking is quite good considering the markets it sold well in are well accounted for. But DD, I am willing to bet a LOT of FH players simply bought it via XBL.

Since some of you seem to be confused, the Aston Martin car is NOT DLC, this is a patch or update therefore the whole multiple account thing is null and void.

Way under tracked in parts of Europe and world, vg cant track it in most markets and their inability to do so is well known. Its a ww seller, to hard for em to track. I haven't played it in a bit and i just got a wheel, to busy with PS4.

With digital its probably in the 5/6m range, It lost about 2m in NA due to no tv commercials but else where it got em, with na being PS3s and Gts weakest market is somewhat makes sense.

a shame there was no PS4 version.

Probably due to digital sales.

Not surprising, remember when they were announcing GT6 and GT on PSP numbers came out from PD and VGC was massively undertracking it.

lol yep, GT5 if i remember was less then half of its actual sales.