I had to go through all the publish notes a while back, looking for when certain ideas/items were introduced into the game.
Of the 56 major publishes, and about 30-40 incremental publishes with notes (there were also a number of them that were not detailed in notes), there are about a couple dozen (mostly incrementals) that were event only.
Two major publishes (not detailed in the notes, conspicuous by their absence) were the ML content publishes. There were similar publishes for the introduction of Tokuno, Malas, Ilshenar, the Tram/fel split, and T2A, if you go looking, so figure about a dozen publishes for these.
About another dozen were ones that incorporated new systems into the game (champ spawns, Smith BODs, Tailor BODs, Paragons/minor artifacts, Personal attendents, etc.)
So, you're looking at about 50-60 publishes (most of the incremental publishes, and about 1/3 to 1/2 of the standard ones) being content driven.
The remaining half of the publishes were 80-100% bug fixes/balances in their content. These ranged from incremental publishes to fix a specific exploit or set of exploits, to full publishes where 1 or 2 new things were introduced, but the remaining 1-3 pages (if you printed the list of changes) were all fixes and balances - and some of them had undocumented fixes that were usually (but not always) edited into the change list after the fact (these exploit fix changes being held back from the list, then announced later, to keep people from attempting mass uses of them before they went away).
The idea that nothing ever gets fixed is a fallacy - it's more accurate to say that many fixes are done in most publishes, but many complainers don't care, because their "pet peeve" bug/balance issue wasn't fixed (and in a number of those instances, the nature of the bug/imbalance is a perception issue, and the game is operating as intended, but that's an entire other issue).
Examples: It took 3-4 years for someone to figure out that someone left a ")" out of a line in the Smith BOD code, that caused certain BODs to drop too often, and others not at all. There are other issues going on with Tailor BODs, that are still under investigation (see the numbers that I've been putting together in the sticky in the UO Craftsman forum). Then there's the perceived imbalance (that really does need addressed) that 1 out of every 25 tailor BODs dropped is a small for a Barbed kit, when the equivalent Smith BODs (for Verite/valorite hammers) drop about 1 out of every 1000.
A lot of the situation is more perception, than anything - and every profession has its blinders that focuses on too tight an area for "change" to note the massive changes going on in other areas outside their focus.
After all, I'm sure the only people in the PvP arena that noticed how massive were the crafting/runic changes in February, were the ones that crafted their own weapons (or to sell to other PvPers) with an alt.
Similarly, the nature of the coming champ spawn changes have different levels of meaning to crafters, PvPers, legitimate merchants and dupers.
You can't please all the people all the time...
So in essense that's 2 patches that fixed stuff, and 1 for content...