The change log for Retribution indicates that the galaxy sizes have been increased. No other information is given. In the section for Crusade, new map sizes for the four smallest galaxies are listed. There is no indication if they are the same as those in Retribution. I have played on Huge and Immense galaxies in Retribution, and they seemed to be substantially larger than in Intrigue.
I decided to check the MapSizeDefs.xml file in Retribution to see the actual sizes. I was surprised at how big the new sizes are. Even Ludicrous has been increased. I have compiled the sizes in Intrigue before the update and the new sizes in Retribution in the table below.
The size of a galaxy is determined by the HexSectorSize (or HSS), which is the number of rings around a center hex in a hexagon made up of smaller hexagons. The total number of hexagons (or hexes) in the galaxy can be calculated from the HSS. I first learned how to do this from a comment by zuPloed in this post. I simplified the equation and have been using it since then. I have made this drawing to show how it works.
Here is the table showing the HSS and Total Hexes for the previous sizes in Intrigue and the current sizes in Retribution. The last two columns show the increases in percent, which have some really big numbers.
If you have trouble playing some of the larger galaxies, now you may have an answer as to why.