Its not entirely true....Ex : jyothi -jyodhi(Tamils say jodhi )..mantri -mandri..lokam -Logam..antham -andham...kataaksham-kadaaksham...tapassu -tabassu etc etc.
pronunciation depends on geographical variations/religion/caste in Kerala...for eg---Sanskrit. word Bhaasha(language) is Bhaasha in standard Kerala Malayalam,Baasa in Lakshadweep Malayalam,Baasey in Kasargod Malayalam and Paasai in paraiyar language (a tribal dialect of Malayalam)..