I personally think it varies from person to person. For me, the majority of the blogs I make will be sold on after a week or two, and there are periods where I won't own any sites for about a month, so, if possible, I'd rather not be paying for months I'm not using.
Also, I don't know where I'll be in a years time. I'm just moving to college, so the amount of time I have might drastically reduce the amount of time I spend blogging. I personally wouldn't want to make a committment as big as a year.