I'll admit that I know almost nothing about the ways DRM works, but my gut tells me that JS would be too slow to implement anything too robust. If DRM is anything like crypto, wouldn't it require something relatively CPU-heavy?
That said, I didn't know the cross-platform thing was optional, and I agree that when I buy something, it should be DRM free. If it has to phone-home, then I don't own it, and things like Darkspore prove it can be stolen from me be the company.
DRM isn't really comparable to traditional crypto in the sense that crypto is intended to protect your secrets from anyone who doesn't have the key, while DRM is about preventing someone with the key from copying the unprotected content (since the content needs to be decrypted for consumption). As such, CPU-heaviness should not exactly be a requirement, as the cryptographic strength of the protection itself isn't necessarily the most important thing.
