Agreed but I think situations are arising which can force the sale. If we assume from an ROI perspective that it continues on a negative trajectory for TASM3 (2016), a reboot post that movie will be 4-5 years away. Sony is not flush with cash these days and a lot of their divisions are not doing well. (Excluding gaming, movies, insurance/finance, etc) If they do decide to reboot, they won't have positive cash flow from Spidey for those years and have to depend on other sources to finance their movies. The other sources of money may not be readily available since they are utlizing a lot of debt to turn around their main businesses.
Plus Wall Street is already harking Sony to spin off the movie division which would only increase the pressure the new spun off company to sell it back so that they can finance other movies. (Maybe go after Bond which has been doing quite well). Again alot of hypotheticals but not impossible.
Either that or I am just coming up with crazy rationales so that Spidey ends up in Marvel's hands.