Check CPUID presence

Hello, i have little question. To detect if CPUID if present, OsDev website recommend this code:

Code:

 pushfd                               ;Save EFLAGS
    pushfd                               ;Store EFLAGS
    xor dword [esp],0x00200000           ;Invert the ID bit in stored EFLAGS
    popfd                                ;Load stored EFLAGS (with ID bit inverted)
    pushfd                               ;Store EFLAGS again (ID bit may or may not be inverted)
    pop eax                              ;eax = modified EFLAGS (ID bit may or may not be inverted)
    xor eax,[esp]                        ;eax = whichever bits were changed
    popfd                                ;Restore original EFLAGS
    and eax,0x00200000                   ;eax = zero if ID bit can't be changed, else non-zero
    ret

I understand all except AND instruction. Why use AND instruction set EAX to 0 when ID bit can't change ? If i understand good AND instruction, bit set to 1 only if all compared bits are value 1. But all eflag bits don't always have bits set to 1, no ?