Question on lithophytes and lime

[OrchidThief79]

I recently acquired a Phal. maculata and was informed that it is a lithophyte in nature and would benefit from a "top-dressing of dolomitic lime". I have a more generalized question on the use of lime/limestone in growing lithophytes.
What exactly does lime do for the plant? Is it used mainly to buffer the growing medium to prevent acidic conditions? Or do these plants have a higher-than-average need for the nutrients in the lime, ie calcium and magnesium?
Also, would it be better to incorporate the lime into the growing medium, with the addition of some limestone pebbles maybe, or would a periodic sprinkling of lime on top of the medium be better? Thanks.