I used the flightstats data frequently, and had no problem with the site. However I imagine each hit of the data was costing a far bit, and the adverts barely convert the cost. With a large number of people accessing it without loading the adverts flightstats were simply subsidising people who were willing to pay, just not willing to pay the right people.
The KVS model is like buying and selling pirate DVDs. Worse, as someone is actually losing out every time you did a search on KVS.
Like HiDDY and many more I assume LVS was a legitimate service, and had it actually run on a modern platform (I.e. Anything but windows) I may well have subscribe in the past. That was before I knew of the imorral business it really is.