Can you elaborate more on the impraticalities? Is it simply a matter of time spent, years vs. a few days, or are there other things involved?
I think Chris reiterated my point wonderfully. In terms of mere financial backing, it's rediculous to expect a web writer to have the same amount of resources as a multi-national, big name publishing company. Most individuals don't even come close to earning in a year what Tor does in a month. As such, we simply don't have the staffing that dead tree authors do. This includes, but is not limited to: editors (freelance novel editors run into the thousands, for instance), promotion staff (think of the people who do the ads, talk to bookstores to get the book on shelves, book tours, etc) and illustrate our works (which can range in the hundreds for book covers, more for a fully illustrated piece).
I'll try to elaborate a bit more below, in terms of the other issues.
Don't other writers also have that same amount of "output, dedication, and inability to succumb to writers block" ?
Not in the same sense, no. Are dead-tree authors dedicated? Sure, but in a different sense. Their process requires a different sort of dedication than that of a web writer who has to make sure to their daily output is postable. Dead tree authors can have an off-day or two without it setting back the whole process in the same way that it would with web writing (hiatus/missed post versus just working extra-hard the next day).
Also, with dead tree authors, it's more like dedication to their job -- they're getting paid for their efforts. Web writers can expect no income from their pursuit, so they have to be extrememly dedicated to take the time away from other activities (including possible jobs) to work on their stories. On the other hand, web writers don't have to worry about upsetting the people signing their paycheck (unless, like Alexandra Erin, they do this as a full-time job). So it's a trade-up.
The processes are just too different to properly compare, IMHO.
As for the output-time ratio:
Sure, it's been said that Stephan King writes around 1,300 words per day. But he doesn't have to promptly post those. He has a long and elaborate process to catch mistakes, to relax and re-edit, etc. Many dead-tree authors write and rewrite for months. Then they have a content editor to look over the general work for consistency, and then a copy editor to examine it further for typing and SPaG errors. During this process the manuscript is then sent back to the author for revisions at least twice before moving it on, generally giving the author at least a week to make the revisions and send it back each time. Around this time the cover art is done, a preview copy is examined, and any other errors are pointed out -- another process that takes at least a week (during which, writer's block could feasibly claim the author for several days without it neccesarily spelling doom). Finally, the finished copy is taken by the publishing company and held over for awhile until it's release date (which can be anywhere from a few days to a few months to a few years).
Now, compare this to a web writer, who has to write 1,300 words each day. They then get a few hours to examine them, edit them, illustrate (if neccesary) and then re-post. It's much more stream-lined; it expects the author to also be an editor, illustrator, publicist, etc. There's very little room to maneuver when they have to find a way to use almost every day's output. It's also not fair to expect the author as an individual to be as good as a highly specialized, well-paid, team that has weeks to months to examine a single piece.