The G70 has less styles and sounds I think but 76 keys. The E80 is Rolands latest technology, has some new styles and sounds but only 61 keys but it has speakers. The operating system and features possibly offer more than the G70 but I've not seen one yet to confirms this, although I intend doing so as soon as I can.
For the price difference the G70 looks to be a great buy considering the new E80 styles are available on the G70 forum for downloading and tweaking into the G70. I suppose it depends if anyone wanting to purchase a Roland requires speakers or not and 61 or 76 keys. At least Roland gives the option to purchasers as to buying 61 or 76 notes. I'd like to see Yamaha do this as I love my T2 but 61 keys is just not enough for some songs.
I'm guessing that the speaker system ups the price on the E80 as it looks very good on the specification.
The E80 is also selling for around £2000 cash price in the UK so a nice saving off the rrp.