Exactly, one clogs and the other doesn't. One has a good design and the other doesn't. And we don't need Epson's data base to figure that out.
John, yes to an extent, but two considerations. (1) There is anecdotal evidence and scientific evidence. And (2) there can be different design purposes with different trade-offs. Epson has not been exactly forthcoming on the latter point, but bit by bit, even from them informally, evidence has developed that this is a significant factor.
A moment on factor (1), the anecdotal evidence so far is quite clear that the 3800/3880 design is very much less clog-prone than the 4900 design. But what really matters is the overall user experience on a large number of units, and only Epson has that information. It makes a difference to one's perception of reliability if the fatal clog rate, for sake of argument, were 2% or 20% - we don't know. As a consumer, I'd buy at 2% but not at 20%, because the risk differs hugely.
Turning to consideration (2), having produced such a successful design in the 3800/3880, why several years later produce a machine that arguably performs less well in this respect? They aren't dumb so there had to be a reason. As far as I can put it together, the reason is that the printhead is designed with twice as many nozzles per sq.in., (yet more dot placement accuracy), the lines are much longer because of the machine design to accommodate a roll holder and larger ink tanks - in other words - the 4900 is a higher-end production machine, and from what I've heard, incorporated these design features with the intent and presumption of the machine being used at high frequency. Any design has a set of a assumptions and trade-offs, and I think we now know what they are comparing the 4900 and 3800/3880.
The upshot is that people who will print infrequently, don't need a roll-holder, live in drier climates without humidifiers and don't need the latest and greatest colour gamut Epson offers should buy a 3880. People with the opposite conditions should buy a 4900. Assuming what I'm saying here is correct, I think it would have been in Epson's longer-term interest to have made all this very clear to the market from the get-go.