This poll is a reflection of people not understanding the nature of the internet (it is 40 parts "normal" depravity, 40 parts extreme depravity, 10 parts mall, 5 parts library, 2 parts TV, 1 part political rally, 1 part music concert, 1 part other) and not wanting to take responsibility for their children. They don't want to take on the work (and negative blowback from their kids) to provide supervised internet access. It's also a reflection of far too many people in this country not understanding what the purpose of government, particularly federal government, is supposed to be.
Trader, you mention that the government regulates TV. This is true, kind of. They actually depend on broadcasters to regulate themselves according to the rules they set. They don't actively filter broadcast signals' content or cut transmissions or anything like that. The regulation is entirely up to the broadcaster to comply with and its only force is that which is afforded the government under legal challenges, the willingness of the broadcaster to comply with those legal decisions, and ultimately the government's ability to destroy the broadcast transmitter(s) if push came to shove. Same goes for cable and dish broadcasters and networks. And the V-Chip almost didn't make it into law. It has to be disabled by default and the ratings of shows and the system's administration are entirely done by non-government groups. I also think it is not a requirement that a broadcast have a V-Chip readable signal embedded in it for any given content (likely would be considered high rating content as a default), but I'm not sure about that.
So TV is really far less regulated than you may think, at least in terms of "mandate" and enforability that you suggest be applied to the internet and operating system software.
That aside, the Internet is not TV or radio. If you want to apply a TV broadcast metaphor to it, then it is much more akin to raw satellite feeds (not Dish or the small sat variants that have shown up in recent years, I'm talking the old 5-10ft sat dish in the backyard). There are literally thousands of channels from all over the world available with no standards except those from where the channel originates (and sometimes not even then). The US government has no control over it at all. Another good example would be ham radio. Worldwide reach, no real standards except those that a transmitter choses to abide by (mostly tech heads and old timer geeks doing it though, so it is pretty tame), and impossible to filter for content on a national basis without draconian and highly expensive measures.
If you're talking about mandating nothing more than a pre-installed content filter, what's the point? People that care about it now have free and pay software available to do this already. Web browsers have some capability built in already. If it is turned on by default, what's to stop an irresponsible parent (or one that trusts their kid, rightly or wrongly) from simply turning it off. You aren't really any further ahead than you are not. If it is turned off by default, you really aren't any further ahead than you are now. If it is undefeatable (always on, can't be turned off), then it is a 1st amendment violation on its face and just forces people to move to "hacker" OS's like Linux where no one is going to be adding any filters, mandated or otherwise.