Well, without entering into discussion about value of Roland UK numbers, all wave-ROM values are correctly designated, megabytes are shown as MB, megabits as Mbit, and gigabits as Gbit.
Of course knowing correct size of wave-ROM doesn't always tell how good the sound is (although the general rule is: bigger memory - better quality), because memory size doesn't tell you how big each sample is, how big is the compression, etc...
As for the E-60, I don't know exactly, but I read somewhere that most of the samples in E-60 are mono, while majority of G-70 samples are stereo, that alone makes noticeable difference in wawe-ROM memory size.
I totally agree with horse power analogy. ;-)