Range is only one factor in gearing. Probably the least important one as well. Compare these two gearing patterns. The lower one is the gearing I currently use on my touring bike. Both have the same "range" but it's pretty easy to see that if you went to that extreme, the shifting pattern on the double would be almost impossible to use. The transition from one to the other is too extreme. In essence, the bike is equipped with 2 independent 9 speed systems.

So let's go to a more reasonable double. But which end of the range should be sacrificed? Keeping the low at the same point...I really like having a super low gear... and assuming that some overlap between the two rings would be good, a 32/20 would be a good choice. But, if you look closely, I'd be coasting at a bit over 20 mph. That's way too slow for downhills.

Sacrificing the low end, I could use a 46/32. Frankly, my knees hurt just looking at that one.

Of course I could pick a more middle ground but then I lose the low gears and the high gears. Of course just staying with the triple, I can keep the high, keep the low and have lots of choices in between. I don't see that a sacrificing anything.