A company's valuation is based on discounted expected future earnings.  With bitpay you have to look at how much will they be earning next year, then the next, then the next?  We already know that their revenues grew 10x last year.  We've also heard that BitPay is presently making buckets of profit.  Bitcoin hasn't even began to hit consumer adoption yet, so if the trend continues then there should be many years worth of exponential growth with a high profit margin.