1 - Not all BD disc can be ripped by all PC. Similar to PSP & NDS's firmware, new BD disc keep update their encryption method, so the decryption program needs update in order to rip the latest BD disc.
2 - Ripped file "may" not exactly the same as the master copy (but 99.99% case are the same). This is because the file stored on the BD disc is not the same as computer data stored on BD disc. There's not enough checking digits (CRC, hashcode, parity bit, whatever) to 100% make sure the data integrity. This is because video data by design is to ensure smooth playback, not accuracy playback. There's mechanism to check data integrity and some data correction, but the aim is to try the "best effort" to recover damaged data "without" delaying the transmission of data stream from disc to TV screen.
So, if the data ripped has some error (not 100% match with original data), then no matter what player you play, it must be some defect compare with the master copy. But if the master copy can be ripped to file without error, then I am sure that there is no difference. The difference in picture quality is mainly due to the video decoding hardware, that is the media player you are using.