[ancymon]

Are they are just running Nominatim? Is Nominatim reliable? Looking at Nominatim project on github it does not look like well maintained software (e.g. there is even pull request from 2012, issues with basic use cases)...

[rmc]

Nominatim is actively developed, and in active use by many organisations to handle large load. It is reliable.

[gopi_ar]

We use a more stable version of Nominatim internally and pushed that out with locationIQ. :-)