I'm going to risk being offensive here, but I think we should not mourn the 'dying breed' too much.
I think that the percentage of DM's that craft alot of house rules is falling because, many DM's have realized that thier talents as a DM don't lie in rules smithing. And rather than getting pretentious and looking down on DM's that don't smith thier own rules, I think we should commend them for realizing thier limitations and playing to thier strengths.
Rules smithing is hard. Good rules smithing is very hard. Even good rules smiths turn out more junk than quality. I know for my part there have been things I wanted good rules for 15 years now, and despite 3 or 4 iterations I still don't have a system I'm proud of. So I either ignore it, handle it by fiat, or rely on some one elses rules. And I consider myself better than average when it comes to inventing ideas and smithing out rules for new content.
I've known alot of good DM's that couldn't rules smith there way out of a paper bag. They are plenty intelligent or creative people, and they run enjoyable campaigns but for whatever reason they just lack a knack for understanding what they want a rule to accomplish, what the consequences of a particular rule will be, and how to obtain the result that they want elegantly. The house rules forum is filled with threads by very well meaning and intelligent folks, who created a bunch of rules that don't accomplish the thing that they set out to accomplish - or indeed were written without any clear goal at all just that they thought it would be 'cool' or (shudder) 'realistic'. I'm as guilty of that as any one, its just I made most of the obvious mistakes 10 or 15 or 20 years ago.
And I think that that is the reason that rules smithing is becoming less ubiquitous. The guys smithing rules for a living today have the benefit of 20-30 years of hindsight and experience with gaming 'technology'. The rules in most RPGs out today are pretty tight and for the most part elegantly accomplish what they set out to accomplish. And for D20, there is alot of ideas out there. So there isn't nearly as much reason to smith out your own rules, and frankly we should be glad that there isn't.
That said, I still make alot of my own feats, magic items, and monsters. Like the Jolly Giant, I agree that there is a big payoff to the metagame if the players don't know everything ahead of time. I've always been of the feeling that there are some campaign secrets which are too important to publish, and that the answers _must_ only be known to the campaigns DM if the full impact of revealing the secret during play is to be had.