The UK edition of "Green Acres" Season 1 fixed the 'flipper' problem with 4 single-sided discs. I've avoided buying Season 2, but yes, Season 3 is on single-sided discs.
Back in the 'day' flippers were regarded as space-savers, but in the days since, it's become cheaper to simply manufacture everything in single-sided discs (and packaging has more options as well).
I can only hope that "Dallas" is being reissued on single-sided discs. I haven't been keen to buy any further sets (beyond Season 1/2) because of the flipper discs.
Mill Creek is using the hub cases for their reissued Sony sets. I don't mind them much anymore, to be honest. In the beginning I always repackaged the discs in proper 'flip style' cases, but now so many companies are using them, and I haven't noticed any particular wear on the discs to rehouse...
In the UK there is a Complete Series boxset of "Dallas", all on new single-sided discs. I'm not sure if it has been mentioned in this thread before.
http://www.amazon.co.uk/gp/product/B007N0IKKM/ref=ox_sc_sfl_image_1?ie=UTF8&psc=1&smid=A3P5ROKL5A1OLE