Generosity means that you are giving to be nice. If you are giving from a place of being nice you shouldn't expect anything in return. However, manners and being polite and appreciation for what has been given to you should make you want to give back in return. If you don't, the person may no longer show you generosity.
When you do something generous it feels good and it is the right thing to do. And, when you do it, you should not expect reciprocation because that makes it look like you were just doing it for personal gain. We all have to take the attitude of selflesness in this world.
We work and we expect to earn in return, we serve for some one or something and we expect to earn in return, we sell to get money in return, and we sometimes even talk and transfer some information to other people to get money in return, these all are considered reciprocal situations that we all human being live along to survive. But some time in life it happens that we sacrifice ourselves to our conscience, some times we stop thinking and submit ourselves to our feelings need. Some times we give because we feel that others need to live as well. This is why we don't want to get any thing in return and that is our *generosity.*
Generosity is something best offered with no strings attached. If reciprocation becomes expected, then generosity becomes less of an act of selfless help, but a business arrangement, and therefore should be called something else. The beauty of the concept of generosity is in fact its freely given nature and that nature should be respected and upheld.
No, not all acts of generosity should expect reciprocation, because that is not why people help others. Act of generosity help the entire a community. It might not be the person that helps you that will pay you back. It might be a pay it forward situation. But the most true help is the help that is given without expectations.