I can understand that you need different cartridges with different chips for the r220 and the r280 but what about bulk ink? Since both use the same colors can you buy bulk ink to work in both? I would think the black dye ink used in the r220 would be the same as in the r280 but I have not been able to google and find a answer to this

http://www.inkbank.com.au/category30_1.htm

I found the answer at this site

Find the right ink to use with your Epson or scroll down to buy...

E 5 (dye) is our most popular refill ink for Epson printers. It is great for printing anything from plain paper documents to high quality photos in all Epson printer models. The E5 is also suitable for printing onto printable CD's and DVD's, T-shirt transfers, matt and gloss inkjet labels and most other inkjet media. E5 can also be used in "Claria" printers, but the prints don't look quite as bright or sharp as with Epson "Claria" or E6 ink.
Available in: BK,C,M,Y (4 colour printers)
BK,C,M,Y,LC, LM (6 colour printers)

E 6 (dye) is a new ink for Epson "Claria" printers such as R270, R290, R380, R390, RX590, Photo1400 &1410. Closer colour match (than E5) makes it the ideal substitute for Claria. Other properties are similar to E5. Great for photos, CD's, DVD's etc, but don't expect any higher fade resistance with this ink. E6 can also be used in older (pre Claria) Epsons, but there is no noticeable improvement in print quality. If anything, the colours are slightly less accurate.
Available in: BK,C,M,Y,LC,LM

E 8 (pigment) is a direct replacement ink set for R800 and R1800 printers. High fade resistance and works great on most inkjet media including gloss paper. The ink set includes 2 blacks, red and blue inks plus a clear gloss optimiser (GO). This ink set is not suitable for any printers other than the R800 & R1800. Note: The GO is not as glossy, as the original Epson, so if you want the highest gloss prints, use the Epson original T0540 gloss cartridge with the E8 ink set.
Available in: MK, PK, C, M, Y, R, B, GO

The R280 is supposed to use a different ink to what the R220 uses the Claria ink is supposed
to give you a better quality print that is supposedly water resistant on Epson photo paper but
I suppose it would work in both for normal printing needs at least I guess it would any way.

Yes that what I got from the site above it looks like either ink will work in the r220 or r280 just will loose a little quality if you use the r220 ink in the r280 but I am willing to bet it will be so little from reading this article that for every day printing it would not be enought to notice. As for as using the r280 ink in the r220 from what they said it will not help the print but that all. I Will buy only r280 ink from now on.

IMHO, the "Claria" inks are worthless, and no different from the rest. I could never see any difference here, and it's anything BUT "smudge-resistant" as they claim. No difference in color matching or intensity either. Use any decent dye-based ink you like.

yes if you read the info at the site it says that the smudge-resistant
claim is hard to prove

I use a continuous ink refill system with my R260 and get great printing using the pigment ink.Save's lots of money.