I went into SFO r28L last week, no glide slope, and no papis visual approach only and the DME doesn't read 0dme at the threshols!
Emphasis is mine. This appears to corroborate the PAPI being OTS.
But, immediately following it:
Conducted LOC approach into SFO last night, glideslope out of service for both 28R & L due construction (until August 22nd) , PAPI was working last night. Departed this morning in relatively calm winds, visual approaches were in use for the 28's.
This is a more recent report, so I'd put more credence in it.
It was followed by:
Confirm no G/S on both 28L and 28R. PAPI only
and:
Departed SFO yesterday, no VASIS, PAPIS or ILS at KSFO. Only G/S available according to NOTAMS is what's in your FMS.
A number of people posted the NOTAM saying the SFO 28L PAPI is OTS, but others followed up and pointed out that it was date/time'd AFTER the crash.
The entire thread is here: http://www.pprune.org/rumours-news/518568-asiana-flight-crash-san-francisco-26.html
So, it's looking like there is some confusion about whether the PAPI was actually OTS. If these reports are accurate, its status was changing, right up until the crash.
A number of posters to that thread added an interesting claim: PAPI/VASI was required for a visual approach. They had various qualifiers: air carrier, night, over water, etc.
It wasn't clear to me if it was a government regulatory requirement (not the US: UK, Italy, etc.) or a company requirement. There were some challenges to their statements, and I didn't try to sort through all of them.