I think Sony and Apple both wanted to create a mini cable network via the web as a direct competitor to cable service. More like a new cable market, but more cherry picked.
The back end service isn't an issue for Sony. It's content partners. (Sony owns a large chunk of Hollywood, in case you forgot: film, tv, etc.)
Do you know how many cable channels are owned in full or in part by Cable providers? The ones who aren't also would have to feel the wrath of Comcast and TWC, and others. Then we get into the fact that the content providers who are free and clear to do what they want still charge a hefty fee to cable operators that they're going to want to charge to Sony/Apple or whoever.
Do cable companies gouge us? Absolutely, but their weighting costs do come down to what they pay to content providers. This is why you see cable providers buying or investing in networks. It cuts their costs, and allows them to profit off of their competitors who need those networks.
Then you get into the muddy issue of needing a really fast internet connection for such a service. (So you still are giving a cable operator money anyway, and cable companies charge a premium for their internet services if you don't subscribe to their TV offerings. So much of a premium, that for $20-$20 more, you could just have a full package with them. Comcast will charge you around $70 for internet alone at a decent speed. Slow connections don't make for great TV over the net.) If Apple/Sony really wanted to compete, simply streaming content would never be enough. It would need to be real time, and providers are not going to want to circumvent commercials that make them the bulk of their money.
I think if any companies out there would ever consider such a thing, it's not going to be network tv (cable or broadcast). It would be subscription channels: HBO, Showtime, Cinemax, Stars, etc. They would be the only group that would have nothing to lose and everything to gain.
HBO doesn't allow web subscription even for their HBO app because they have contract limitations with cable operators, and I'm sure the others do. Now when those contracts need renewed, maybe that could change.
It will always come back to money. At the end of the day, advertisements are the bread and butter of content providers, and any model that wants to cut that gravy train will never fly.
Now Sony actually has a leg up on Apple. They OWN a crap load of content. Sony Pictures owns MGM now, in addition to Tri-Star, and several other groups they've acquired over the years. They also own tons of television shows, and music resources. Where Sony has a chance that Apple didn't is they have something to bargain with: their own content availability. They could also launch a service exclusive of their own content.
So will we see a service from Sony like the rumor suggests? I doubt it, but I could totally see a Sony service with a great bulk of content in it that might be compelling enough to subscribe to.