There was never any that much hardwired functions for F1 and F2 on PC (apart for the convention that F1 is almost always help).
On the other hand there is a related issue: on DEC (and some other) terminals with LK201-style keyboards (which in turn inspired the "modern" PC/AT keyboard layout with F1-F12) the keys in positions of F1-F5 had fixed functions. This is the reason why there are about four different escape sequences across vt220-compatible terminal emulators for F5. There simply was not any DEC terminal that had F5 on its keyboard (F1-F4 are almost always mapped to PF1-PF4).
