True in the case of Nasri. The market value of a player is not based on what someone payed for someone else a year ago. It is what the market is prepared to pay now which is influenced by the economics of the clubs, the potential new 'fair play' rules, the length of contract remaining, how much the buying teams need exactly that kind of player to complete their kind of setup, etc. etc.
It might well be that Cesc has a maximum price of 35M. We might want more but if no bugger will pay it then saying he is worth 50 million is meaningless. For us, it is a question of whether 35, 40 or whatever will enable us to sort it out once and for all, and to have enough money to buy who we want. I presume some of the clubs with players Wenger wants are holding for what they can get - they want to get an idea of how much we have in the pot and how much we will get for Cesc / Nasri so they can work out at what price they should settle.
Like I keep saying, the transfer window shit just fucks things up. Without a window deadline, people would just deal with one player here and there as needed and this complex crap would go away.