"There is an RNAV GPS Approach available for R28L
They could have programmed the FMC and followed LNAV VNAV right down to the runway if they had wanted to."
Apparently RNAV GPS with WAAS augmentation was available at SFO and provided an artificial glideslope. The out-of-service GS was planned and the RNAV GPS was provided as an alternative precision approach -- including vertical LPV guidance. See FAA bulletin, section 4:
http://www.faa.gov/documentLibrary/m...N_8900.216.pdf
"For about three months in mid-year 2013, the FAA will render the LDA for runway 28L and the ILS for runway 28L out of service (OTS) at San Francisco International Airport (SFO) due to runway construction. The loss of these navigation aids will eliminate the ability for SFO to conduct PRM approaches during simultaneous offset instrument approach (SOIA) operations. The FAA plans to publish RNAV (GPS) PRM procedures prior to this navigation aid shutdown."
RNAV GPS background:
http://www.faa.gov/about/office_org/...l_06122012.pdf
So the inop GS need not have affected Asiana. They had equivalent vertical guidance available (ie an artificial glideslope), had they chosen to use it. If they didn't feel comfortable hand-flying, they could have made a fully-automated approach. The equipment was available.