I have to say that, for Famitsu to say the disc is 19gb+, they would have to take the disc and insert it into a PC with a Bluray drive installed, wouldn't they? Konami wouldn't tell them that information (if they had, you could be sure it would say "OFFICIAL FIRST INFORMATION" all over it and have quotes from Seabass).
And bear in mind that even if it's true, 19gb now doesn't mean it won't shrink dramatically when it's compressed. 19gb is a BIG number - even if you had twice the number of teams (team-data is very, very small) and high-res kits for all of them, it wouldn't amount to that big a change, no way in hell.
If you extracted every single image, soundbyte and all the other files from WE10/PES6, you would have more than 4gb of information, that's for sure (I've got a folder on my hard drive containing something like 20-30% of WE9's extracted graphics plus some of the music - I was working on a patch - and that folder alone totals 4gb). And as somebody else has said, Konami always include data from all of the old versions of WE on the disc, which will increase the size again. So it may well be 19gb before compression, but that doesn't mean anything.
Come to think of it, it doesn't actually mean anything anyway - how good a game is doesn't depend on how much space it uses on a disc, and programming doesn't even take up 100mb, never mind 1gb. Put it like this, the guys who hate FIFA with a passion will say (upon the news that FIFA 08 is however many gigabytes) that it doesn't matter how big a disc EA have, they will never make a good football game out of it. So it really doesn't matter.
Just so you know, I'm not a fanboy of either console, or even of PES. I'm just giving my two cents. It's my personal belief that the PS3 will have the better version of the next WE, simply because it's the lead format, but I believe that the 360 version will be the same with the same data (perhaps excluding graphical effects here and there, which I can live with - although I expect I will be getting a PS3 around Christmas time, when the price drops to £250-£300).