Yes you are right but i didnt want to go to technical details too much, PNG is great for low color, flat images when ut can use its full potential of lossless For vivid photo you get better results with JPG compressionwise, As for purist android developers to use the PNG for UI graphics is the only viable solution, for photos i would still consider JPEG as better option.
So you wanna small file on rich photo use JPEG, wanna small file for your UI interface which doesnt look like rainbow parrot with great quality ? use png
png has transparency which is great for us developers, loseless is not 100 perent loselles though , it fiddles with gamma settings and those would have different implementations depends on realization.
Wanna good quality and you don care if image might look little dull? use 0 quality option , wanna see original ? use 9 in gimp for PMG. It has also lotsa options their implementation might not be supported on all platfoms, though PNG is most usefull universal format for us unless you work for National Geographic or PLAYBOY, lol