I believe the 2 year rule applies to assets of the business, not expenses.
For example you could buy a car for business use and that would be an asset of the business, and of course it would last two years. (Hopefully!)
I'm struggling to think of something you could buy that would last less than 2 years but be an asset. I suppose in our business it could be something like a bondage device which with heavy usage might need to be replaced every year. So the purchase cost could be claimed as an expense, but the item would not be an asset.