There is certainly some quality differences in the product itself as Panasonic tends to be one of the class leaders for reliability in the industry. Now, discs offer some online content, which is often not necessary, but moreso, the players need (MUST HAVE!) firmware updates to be fully compatible with the latest Blu-ray Discs which are coming to market.
This is something which other manufacturers may or may not properly support, while Panasonic will generally support very well for years to come.
We aren't talking about a $500 Oppo, but a $170 player vs. a $50 player, and the small difference of $120, IMO, is really worth it to get the quality and reliability which Panasonic delivers. Really, the DMP-BD75 is what I would get from Panasonic if I wanted 'cheap'. Get cheap AND stick with Panasonic for $80. Makes a ton of sense.
Now, when the cheaper player works, it should deliver very close to the same quality as the Panasonic player to most people's eyes. That's not to say it will, but it will be close. But, stick with Panasonic.
You DO want the player online for firmware, so if you must have wi-fi, the 220 is the one with it built in.