This problem isn't limited to Windows 7/2008 or XP. It affects Win10 too.
>especially when the font is merely ugly in a cosmetic sense, and not unreadable
Eh, you won't go very far with this attitude in any design team.
Also, anyone who tried to manually craft font-family fallback path are already making effort. You can literally choose to not assign any font. Actually, it probably works better: most of browsers have sensible default (which often times is system font) already.
My counter-argument would be that even if a platform is EOL, if it represents a serious chunk of your audience then you should probably do what you can to accommodate them. Especially if, as here, you might be able to fix it with a very simple change.
I don't see any reason to make any effort to support those folks, especially when the font is merely ugly in a cosmetic sense, and not unreadable.