1) It's true, I cannot magically produce an entire photo-editing app in two weeks, but this makes the assumption that I won't be very frank with what I will deliver. It also makes the assumption that I can't work with people multiple times. The point here is to define a unit of work. My unit of work in this endeavor is two weeks at a fixed cost. That doesn't seem unreasonable to me. I'm not here to prey on clients and if what I offer isn't a good fit for them, they'll know in our first conversation.
2) This makes two assumptions: that I am doing this to build a client-based business and that I'm in this primarily for the money. I'm not really trying to build a client-based business that works for everyone. I've been a part of such businesses and I really disliked my time there. As such, I don't mind my frankness being a filter for who I do or do not hear from. Which brings me to the second assumption; I'm doing this for the fun of working with other people to bring ideas to life, not to make money. So while my clients pay me, they're getting a good deal and it really is up to me whether or not I wish to continue working on their project. That's not me expressing attitude, that's me being honest right up front. :) Moreover, I believe service is exemplified in action and while you seem to think otherwise, if I take someone on, I'm there to help them the best I can.
3) This hits the same point I made before, if the idea changes, there's no reason I can't work something out with my clients. There's also no reason that we can't set up another two week iteration.
While I understand your points, they seem tinted by negative experiences and though it may sound trite, part of why I'm doing this is because of my own poor experiences in client work.