I'm not an expert by any means, so I may be wrong, but I think there are a lot of "influenza like" virus' that present much like seasonal flu and end up being common colds.
My son and I recently went to the Dr. with fever (the body aches and chills that are associated with having fever) congestion, sore throat, and cough. We were diagnosed with a cold, not influenza.
I have always been told that influenza comes on very suddenly, almost out of the blue, where as a cold or other influenza like illness come about a bit more gradually. I have been told that h1n1 also hits out of the blue and that may be one way to tell if you have flu or just a cold. I am pretty sure that other than that, an influenza test is the only definite sign in determining a cold vs. seasonal flu. They usually have very similar symptoms.
Not everyone who gets the seasonal flu gets fever either. I have a friend who's kids never get fever, though like you said, I think it is much more common for people with h1n1 to not present with fever.
Every influenza strain is different, with varying degrees of illness. My husband received training about this years three strain vaccine and was told that they are strains we have not had in quite some time, people may have lower immunity to them than more recent strains, and therefore have more severe symptoms than with past seasonal flu. This was at a Military base, not a hospital though, so who knows how accurate that info. is.
One thing to consider is that the wide variety of symptoms or disease severity could also be because cold and flu are so similar, and Dr.s are no longer testing most patients for flu. Someone might go to the Dr. with a cold and be told they have h1n1 and someone might go to a different Dr. with h1n1 and be diagnosed with a cold. It's con-flusing!