In a word, yes.

But some flowers, especially double ones, are sterile, so the plants have to be propagated in other ways.

F1 hybrids don't always come true and revert to some less pretty colors or patterns, so it depends.

OK. Let me reword it. In most cases, yes.

Errr, is this question generalising or specific - and i've missed the first part ?

And sometimes flowers simply don't get pollinated, so they don't have seed. In some other cases, the flower dries up, but the seed pods still have another month or more to mature before the seeds inside are viable.