If you play a 'big' team, it's not like they put out their first team and go for it, is it? Whereas arguably against the smaller teams their players are trying to get noticed etc. So you could argue that these games may be just as much of a challenge. The preseason is all about fitness, not so much about tactics. Do you really think managers are going to allow all the scouts from other teams to come and see what's going on? No, they keep that behind closed doors. Certainly formations and other larger experiments would go on, but all the intricate play would be practiced on the training ground alone. This is only a guess, but I'd be bloody surprised if its not how it is.
The reason we started so well last season was not because of the games we played in preseason, but because of the fitness work and training schedules and the fact that we have an awesome squad of talent.