Sure it didn't work with Guitar Hero, that is a casual franchise. Casual players don't feel the need to buy games every yeat. However, milking the Call of Duty franchise might actually work because hardcore gamers will buy the same game with little improvements....after all they are hardcore!

Will Activision milking work? I say it will as long as each Call of Duty has something new to bring to the table (Ex Zombies Spec OPs).

It'll work until something better comes along. Really the only games similar to Call of Duty are Medal of Honor and Battlefield and those both suck. Games like Resistance, Halo and Killzone are great but they are so different to CoD that they don't really directly compete. If something similar but better than CoD comes along like Respawn Entertainment's new game or Bungie's new game it will kill Call of Duty. 

ah. just like rockband beat guitar hero and everyone lost interest?

Yeah basically. Cod wont be beaten until a shooter even shitter arrives (you can probably gather i dont like cod ^^)

COD's pretty damn casual at this point too to be honest.

Tony Hawk fell, Guitar Hero fell... in time COD will fall too.

tony hawk is another sad case. 

Cod wont last that much longer. BF3 will hopefully make an big splash and really challenge Call of Duty 8. If Dice can pull this off well. 

Madden is as casual as you can get and gets bought year after year.

No matter how good a game is and regardless of the genre, if too many games are made that are too similar fatigue will set in and sales will suffer. Some games and some genres are more popular, and even when their sales suffer they may still sell well; but no games are immune from the consequences of too many similar games being marketed.

No they're not the same(i find that very offensive to compare the huge battlefield to the smaller quick CoD)  and no they don't suck

Maybe next-gen CoD games won't sell that much like today.