Using methods like Steam as the main means to provide content to consumers pose more complicated questions that simply can't be answered at this point. Here's just a few of my issues with such a proposed service:
1) Reliability - Will the offered content be available forever to paying customers or does it have a "shelf life" before being archived?
2) Marketing - Marketing is a huge factor regarding the video game industry. Conventionally speaking, a product is marketed to convincing consumers through the usual channels who then go into store X to purchase the tangible product. Not sure if the mindset of Consumer America can be convinced to pay the same price for a "download".
3) Stability - The availability of any given product is only as stable as the company offering it online. Not to mention technical issues with server problems or hackers or whatever. Having these services become mainstream would mean your personal information will be just that much more available to potential hackers and thieves. A lot of people are paranoid as is about shopping online and services like Steam could greatly impact overall sales if it were to be the only method.
4) Console business - Technology and the overall mindset of the console business is very different than that of the PC business. There's still a significant amount of younger people without the proper means to purchase content online yet can save up their allowance or paper route money (or whatever) and still go to TRU and pick up a game they want. Sales would definitely be affected in this regard as well.
5) Sales - I don't see content "going on sale" through these services simply because majority of the major publishers offer their products through their own online stores and how often do they go "on sale"? Not very often, if at all. Target, Best Buy, Fry's and the like are a blessing here providing sales as incentive to bring consumers into their stores. There's no need for such competition with Valve's Steam service. If you want HL2, you use Steam and that it (if there was no retail equivalent, of course)!
6) Trade-Ins - Will not exist if the industry converts to a Steam type method as the main means to provide content. Way too many people have comfort in buying games, knowing they can later trade them back in for use towards a different product. There's also the option of reselling the used game to someone else.
Basically, I think that services like Steam should be nothing more than an "option" to people willing to take that route. I, as a consumer, prefer the traditional method of acquiring any given product I purchase, having something tangible to show for my money.
