I agree that it's better for hobbyists to include a transformer, but I do disagree with some things you write...

A Transformer will RARELY hit 95% efficiency. The reality is a figure somewhere between ZERO (yes ZERO percent efficient!!!) and somewhere approaching 90%. Let me explain...

The higher the frequency, the greater the transfer ratio between the Primary and Secondary. Hence, the most efficient are Switching Power Supplies which usually run at a few tens of kHz. However at the frequencies of the incomming AC Mains Supply (ie 45-65Hz depending where on the planet you happen to be), the efficiency is governed by the amount of iron (and quality of iron) you can shove into your transformer. Generally, the more iron, the greater the transfer ratio which conversely applies the law that the smaller the transformer the more inefficient it will be.

Now for this ZERO percent efficiency (100% waste of energy) bit...

The efficiency of a Transformer is simply calculated as Power Out divided by Power In. Actually we can reduce that to just Current In viz Current Out with regard to the turns ratio. So in a 100% efficient Transformer, 1A at 12V OUTPUT should equal 50mA at 240V INPUT as there's a 20:1 reduction ratio. Sadly, take any Transformer out of your parts box, put a series Ammeter with the Primary and plug it in completely OFF-LOAD. You will have a standing current... ie you are sucking energy in, but not taking any out. All this is doing is heating up the core, and it's worse the smaller the Transformer becasue of the smaller amount of iron. So from this you can gather, that the less current we draw from a Transformer from it's optimum design point, the more inefficient it will be. If a Transformer is designed to be most efficient at say 100mA, then any current draw less than that is heading towards the ZERO efficiency point when it is completely off-load. Likewise if you exceed the optimum design point (which is usually just below the Magnetic Saturation Point of the core), you then risk driving the core into saturation and again your efficiency plumets as all you end up doing is pumping more current in which just heats up the core.

From the above, you can gather that a Transformer is really the root cause of global warming as before it was invented we didn't have the problem!

Notwithstanding that, it does give you galvanic isolation and as proof that countless hobbyists are alive today posting silly questions on internet forums that otherwise wouldn't be, is it's most commendable feature.

Finally, there is a place for everything... even the humble Transformerless design. For small current supplies, the size and cost beats the transformer every time. For a typical Washing Machine or Freezer or Cooker or Microwave or Boiler or Central Heating or Air Conditioning or ..., or... or (add your own domestic appliance to the list) controller, losing the transformer would save about 50 cents (and save some weight too), multiplied by a typical 300,000 production run for the design and you can do the math.

As for hobbyists that play with mains... well we all gotta die sometime (it's a hereditary trait), just some sooner than later...