Hi Tom,
I hear what you're saying. Every vendor sets the prices for their gear based on the features included in their product, so yes, the cheapest lens has the fewest features. The question in this case is whether the photographer actually needs the features and whether those actually deliver a better end product within the shooting regime. At f2.8 and beyond for example, the performance of the 1.2, the 1.4 and the 1.8 lenses will be pretty much identical in terms of sharpness, distortion, contrast and color rendition. There are bound to be slight differences but not that you would see in normal photography. The more expensive lenses will probably be constructed using more metal and will be more rugged and robust so pros would opt for this lens. Since the price of gear is amortized over the life of it's use for a pro it's a no brainer to buy the 1.2, but for us, we're not going to see much a difference in our photos unless we spend a lot of time in shooting regimes like night photography, astro-photography and so forth.
It's the same story with Image Stabilization (IS) and Vibration Reduction (VR). This feature carries a £200-£300 premium but they have nothing to do with the optical quality of the glass inside the lens. The IS/VR version of a lens has the same optical quality as it's non IS/VR counterpart. If you shoot from a tripod you actually have to turn IS/VR off as it degrades the image. So if you do most of your work on a tripod, such as in studio work, this feature is mostly useless. Likewise, if you shoot mostly at high ISOs and wide open with fast shutter speeds, or with flash, IS/VR doesn't help. Hand held, under normal or dim lighting IS/VR are worth their weight in gold.
The only reason I'm so adamant about this is because I use a lot of old and entry level lenses, some of which aren't even autofocus. The lens used on that macro shot example is 15 years old. These lenses have primitive or no microchips and some don't talk to the camera, but metering works and I can focus manually so this is not a big deal. Some of the old lenses equal or actually outperform the newer ones and are more rugged because they were all metal in those days. I see a lot of talk on various sites about how this or that new lens is the ultimate or whatever, and I think to myself hmm.. maybe, from a features standpoint, that might be true but the high prices are a a clear sign of gouging, and optically, old and entry level gear still does a great job. Canon users don't have much of a choice because compatibility issues render old gear unusable on new cameras, but Nikon users are in luck because old and entry level lenses still deliver the goods. The humble entry level Nikon 50 mm 1.8D is one of Nikon's sharpest lenses, ever, while their brand new 24-120 VR is one of their most pathetically softest lenses, ever. Sadly, many have figure this out and prices of used lenses have soared...
All I'm saying is that we ought not to foo-foo a lens just because it's labeled entry level or because it's old technology, because the current technology is more geared towards producing the optical excellence of yesteryear at a cheaper production cost of today. Occasionally we see something that couldn't be produced yesterday such as a high performance wide-to-tele zoom which was unthinkable 30 years ago. We should pay the price of the extra features only if we can't achieve our photographic objectives with the less expensive or older gear.
Cheers,