Have you been stockpiling bitcoin to go on a Steam shopping spree? You'll need to change your plans. Valve has stopped accepting bitcoin due to a combination of high transaction costs (up from 20 cents in the beginning to $20) and "volatility" in the cryptocurrency's value. While the virtual cash has never been especially stable, its worth has taken a roller coaster ride over the past few months. Its value has been skyrocketing lately (one bitcoin is worth $13,300 US as of this writing), but it has also crashed hard -- Valve cited a 25 percent drop "over a period of days" as an example. That fluctuation creates a huge problem if you make a purchase and it doesn't complete before the usual bitcoin price guarantee elapses, as you may have to pay an outstanding balance and a second transaction fee.
Valve isn't completely ruling out a return to bitcoin in the future, although it's clear that won't happen unless bitcoin settles down. There's no mention of opening the door to Ethereum and other digital currencies, either. And no matter what, this underscores a very real problem for cryptocurrency no matter the format. Retailers need predictable costs and payments to run their businesses, and they may be loathe to support technology like bitcoin if it leads to unpaid debts and unhappy customers.