Some poor people name their sons Ian and pronounce it Eye-an, so why should they not guess at Rice for Rhys and stay with it, ignoring or not bothering with the evidence? That is no reason to do it if you take the trouble to do a bit of research and get the right information ... but it's a matter of individual choice. Outside the USA, pronouncing the -th- in Anthony like a -th- instead of a -t- sounds hilarious and is historically incorrect, but at this time in human history it's become a valid option. The same could some day happen with Rhys/Rice.