I think this is a silly debate.
It is a simple fact that XP has unpatched vulnerabilities. It is reasonable to assume W7 does too - or that newly discovered vulnerabilities will be discovered in the future. And it is a simple fact any such vulnerabilities will NOT be patched or fixed by Microsoft.
Not without proper security in place. However, with a solid firewall and AntiMalware suite I have.
Therein lies the problem and why suggesting XP is still safe, and that W7 is unlikely to become unsafe is totally flawed logic. And frankly, I think suggesting XP is still safe and W7 will remain safe is reckless - at least in an open and public forum where gullible novices are likely to see it.
Many security applications no longer support XP. As time goes on, that surely will be the case with W7. Why? Because as time goes by, fewer and fewer users will be using these operating systems. So why should or would any security app company continue to throw resources ($$$$) into research and support for them? There would be zero incentive (read: profits) for them to do so.
So even if a new vulnerability is discovered, neither Microsoft nor the security app developers are developing methods to protect against exploitation.
What does that mean? It means a zero-day exploit could surface today with no chance any security organization will discover it, and protect against it, before your system is compromised by a bad guy.
Most, if not all the major testing labs no longer test anti-malware programs with XP, and in fact, some already don't test for W7. So how do you know your antimalware truly is protecting you from all the XP malware currently out there? You don't. You may have just been lucky and the bad guys have not found you - yet. Same will soon be true of W7. At least with W10, we know Microsoft and all the security app developers are actively looking for vulnerabilities and the malware designed to exploit them. And if discovered, we know Microsoft and/or the security app developers then address those issues in upcoming updates.
So yes, today, as in this minute, it may still be possible to protect obsolete and superseded operating systems from exploits. But all bets are off for tomorrow. And that's why XP should stay off any network that has Internet access, and the same will soon be true for W7.
And for sure, home use is a concern. Most home users are not security experts, nor do they have a security expert watching over their networks.