Your not considering the cost of the plan, nothing is really subsidized, the carriers that offer the iPhone charge more for monthly service, to mostly post-paid users. To make up for the so called subsidy they give.
And your also not considering that it costs more for the carriers to buy an iPhone than the average Android phone. Which is why they are carried mostly on the bigger carriers. prepaid offers iPhones on some plans like Virgin mobile, but the up front cost for the device, means that most users on prepaid choose Android.
Android is very popular with prepaid plans, and post-paid plans, but the fact is that all those prepaid plans drag down the average cost per user.
If you compared only post-paid Android users to post-paid iPhone users, the costs would be much closer.
My wife pays over $80/month for her ATT iPhone. My son and I both have androids and pay a total of ~$65 a month on TMobile. We don't have unlimited plans.
Also, she bought her phone subsidised from ATT. I bought both my phone and my son's phone outright. So perhaps you want to take the $375 for those two phones and divide it out over a few years for a more fair comparison...