I think it is natural that bitcoins are the major basis for comparison.  This might not always be the case, but right now it is the most valuable coin, and the most widely used/accepted.  Most alt coins (including shit coins, because hey, they have at least some value) are not accepted by anyone for payment, so if you want to actually use your coins, you will need to trade them in for one of the major coins, and depending on where you want to spend them, that likely means bitcoins and not one of the other main alts.