I don't know what to tell you. I was involved in 2003, and at that time I used a sort of web proofreading tool that used TIFF. Perhaps that was a feature of the particular tool.
Ah, that may have been the long-obsolete Windows-based client "PRTK."
All the "recently finished" links on the front page are broken not the best way to persuade folks you're not amateurs.
Those offsite links are valid, but not until after PG does its nightly cataloging run which places files in the correct locations on their server(s). Why they don't move files into place immediately on posting a text is beyond me, since it should be trivial from a technical standpoint, but since I don't volunteer for them directly, I can't respond to that. The downside is, as you've noted, that the offsite links we present don't immediately work. In the meantime, we promote our most recently completed works as best as we're able to, given that constraint.
I'm glad to see you've starting using markup to indicate bold and italics. But skimming through your Formatting Guidlines, I see a lot of bad stuff that hasn't changed since I was a volunteer. You still use 4 blank lines to indicate a chapter break. You still use that clumsy, hard-to-parse syntax to indicate side notes and footnotes. And you still hand-format tables! I couldn't find the instructions for entering equations, but I'm guessing you still use Tex syntax to record them.
Your suggestions would work better in a "professional" environment, but in a volunteer environment, they would fail because the learning curve is too high, and more time would be spent correcting difficult markup entered incorrectly. Realize that the markup used at DP is a compromise intended to be rapidly picked up by inexperienced people, and that it is an intermediate format which does not reflect the actual appearance of the end products, regardless of their final format, and especially the thousands of projects which have been produced in HTML.
And in this context "professional" doesn't mean "paid", it means "knows what they're doing".
I'm not disagreeing with your use of the term "amateur." Perhaps you mean to say you disagree with how we're going about the task (and many do, including currently active volunteers). That's how we learn to do this better. Over time, as we've learned how to do what we do, we've refined our workflow and software to be able do it better: a process which continues to this day. You might call it a distributed human genetic algorithm. :)