The bottom line is that things like X-Box Live have shown that people are willing to pay for the abillity to play online, and get DLC and such a little bit earlier than non-paid subscribers. Microsoft is raking in some pretty substantial amounts of cash from this.
Other businesses are foolish not to be thinking "hey, that could be us". Right now Nintendo and Sony have a decent amount of users due to them not charging for their online components (such as they are). However it doubtlessly occurs to both that if everyone decides to charge it's not like gamers will be able to "flee" to the free services. I suspect what Nintendo is doing is sitting there waiting to launch a pay service if Sony (who has talked about doing the same thing) also decides to launch one.
That's what my cynical paranoia tells me at any rate.
Speaking entirely for myself I only rarely buy XBL gold membership (when I have a new fighting game or whatever I might get a month or two usually to try it out online, but gradually I've been gravitating towards just getting all those games for the PS-3 if I can).
To make these fees worthwhile to me, what they would need to do is effectively become their own ISP. One of my big problems with XBL for example is that I'm paying them that money on top of the money I pay for my internet connection. A lot of the features I pay for are things that are redundant with my ISP to begin with... the only thing they really offer despite their "padding" is the abillity to play their console games online.
Now if say Microsoft was to keep their price where it is now, but make it so I could go online without needing to pay for internet... well that would be something else entirely.
Consider that internet is often bundled together with other things like your TV/Satellite/Phone. If say Microsoft managed to make an X-box that did all of these diverse things and offered their service for $10 as opposed to say the hundred dollars a month a decent package might cost you... well... that would be something entirely differant.
There have already been some hints about companies wanting to do exactly that, but none have ever materialized, and what few programs I've seen that were most seriously being considered ultimatly wound up wanting to ask for a price similar to what you'd already pay.
Ah well, enough rambling. The bottom line is that the continued survival of Xbox Live: Gold pretty much shows that it can be gotten away with, other companies were simply more wary about trying to get too much money out of users... online fees however are a cash cow.
