I've been riding a single-speed bike with a 39/15 gear (~70 inch?) in the midlands recently. I'm a couple of stone overweight so I found that a bit tough on some steepish little hills in north Warwickshire. It got me thinking about why people say fixed is easier uphill. Obviously, the 'easiest' thing would be to just use a lower gear but then I'd spin out when trying to go quickly. I can pedal comfortably at about 24 mph in 39/15 which is fine for knocking about in lanes. I freewheel downhill above about 30 mph.
I think the point being made is that if you are a bit overgeared on a climb, it is better to be on fixed than single-speed. After a couple of rides it dawned on me why... I found the problem on s/s on steep climbs was the 'deadspot' at the top of each pedal stroke. My cadence was so low that I was having to use brute strength to get the pedal over the top and get my weight down on it. Once the weight was on the pedal, it wasn't too bad for another 120 degrees or so. On fixed, the momentum of the bike would force the pedals round through the deadspots.
The main thing that puts me off fixed is going down steep hills - I really wouldn't fancy that. I've heard too many horror stories about nasty crashes due to accidental unclipping, that kind of thing.
PS I enjoy riding my geared bikes in Yorkshire, but I have to admit that the single-speed bike is very light and simple (and cheap!) and it is nice to just pedal and forget gears for a while. Easier said than done actually - I find myself reaching for the gear levers for the first 20 minutes or so of each s/s ride.