I personally don't think Steam's an issue at all when it comes to the decline of PC games; the Cloud storage of purchases doesn't bother me in the least, and I think it's a nice jump forward from physical copies. I'll admit, I love having Morrowind and Oblivion for their respective Microsoft consoles in a physical form, if only for nostalgia purposes. Steam gave me those in a downloadable format so I no longer have to tote around a jewel case.
Also this, because active modding communities are the bomb for their work on making console-to-PC ports look even better than before. Pre-Steam games weren't ALL that bad either, hell, I remember my first 95 machine and the release of the previously defunct Presto Studios game The Journeyman Project. But that doesn't mean that I think Steam killed it. The team even came back together recently for a semi-reboot of the brand with Pegasus Prime for Windows, and I still love me some old-school time travel shenanigans (can't forget the extremely snarky AI constructs, either). Can't really bash Pajama Sam, Putt-Putt, and that horribly bad Tonka game that are stashed away somewhere in my house either; my interests changed with time.
More on topic, I think that account-tied purchases has helped more than it has hurt, at least in my experiences. DRM IS annoying though, that I can agree with, and it's probably the only reason why I'm not currently in a rush to buy Mass Effect 1/2/3 from Steam/Origin. Same with Assassin's Creed and UPlay. So no, I won't blame Steam on ruining PC gaming, because the companies are the ones implementing DRMs and being annoying.