The missing point is that of the market demand. DRM is out there, it's too late. It will be used anyway, with flash\silverlight or what have you.
So, this demand should be answered, using flash is no overhead for the site, but rather a bad thing for the end user. not implementing DRM isn't hurting the sites wants it, at that point, it only hurts the end users. so implementing it is the right decision.
Flash is out there and will be used anyway. Luckily since mobile devices didn't (iPhone) support is or supported it badly (Android) it became out of favor. This was eased a lot by the situation that many people already disliked Flash in their browser.
May DRM become out of favor, too. Thus as a first step, you - as a customer - should never accept websites that use any DRM mechanism. Write to their customer support and if they don't offer a DRM-free version cancel subscriptions. Closing your purse is a powerful tool.