Why so many library webmasters haven't switched to CSS-based layout

One question I've heard from time to time is why some webmasters don't just ditch the table-based layout they've traditionally used and go with all CSS-based layout. This is particularly true of library web pages. I'm here at a NELINET Advanced CSS workshop and really understand why we haven't migrated.

(1) need to support even the oldest browsers;
(2) all of the knowledge and time needed to work around inconsistencies in the way various browsers implement CSS - particularly, in relation to the "box model"

I'll give you my synopsis of the "box model" issues in my next posting.