Everything is relative, it's all based off of available space, bioload, etc.....
The other thing people don't factor in is that tank dimentions for a given volume, especially for the smaller tank sizes. People are starting to realize that certain species need a given amount of swimming room to thrive, but they still tend to give the inch per gallon rule, which was based around standard tank sizes, limited filtration, and extremly light (if any) plant stocking.
With tank some of the tank dimensions available today, you can get a long shallow tank that has more swimming space than a standard tank almost twice its volume. Or a tall "cube" that has far less horizontal swimming space than a similar volume tank and may be unsuitable for some species that would be fine in a standard tank of the same, or even slightly less, volume.
It is easier to provide extra biofiltration by doing things like running a larger filter with the impeller from a smaller version to limit flow, adding additional media to the filter, running some of the newer chemical filtration media...
Also heavily planting a tank helps take care of the nutrient issues (most people here end up dosing anyway), although it does nothing to reduce other waste products that may still build up in the water over time if regular maintenance is not performed.
I think people are a little quick to jump on others for stocking levels without understanding the setup that the individual has or what their plan is. Not that being conservative with stocking is a bad thing, but saying that 6-8 micro fish should be the max for a ten gallon might be excessive when those fish max out around 3/4" and have a lower bioload per inch than larger fish. If the tank is stocked decently well with plants and the individual is interested in more than just plants or the plants are there to just provide a more natural look (ie are not the main focus), they will more than likely get bored with a tank so sparsely stocked that they rarely see the fish and as a result, the fish will suffer from a lack of attention and maintenance.
I agree that 20 neons in a ten would be a bit much, but 15-20 micro rasboras in a well planted tank (once it is established) would be fine. They don't school like neons, but they do shoal and hang out together. A couple micro algae eaters would be fine as well if you find you need them down the road (some do better in groups of 3-4 or larger, so you need to pay attention to that as well).
Sorry for the rant, recommendations based on tank size is something I have been thinking a lot about lately. People are coming around quicker with lighting recommendations (shying away from watts per gallon), but still seem to be fixated on the fish per gallon rule and jump on anybody that goes over it no matter how experienced they are or how heavily their tank is planted and filtered.
I mean, an oscar in a 10 gallon fits within the inch per gallon rule. That is barely suitable for an emergency hospital tank for a juvenile oscar. Three mollies in a 10 is less than ideal, more so if you have more than just males or just females. Having two females and one male can result in over 100 fish in just a few months if you don't leave the juviniles in the tank for the parents to eat the majority of, not to mention a standard 10gal doesn't really provide sufficient swimming room for fully grown mollies.
Granted, an inch per gallon is a decent general starting point if people are sticking to the average tetra stocked tank that mostly has egg laying fish in the 1.5 inch range, otherwise it really doesn't work in my opinion.
Seriouslyfish is a pretty good resource that lists fish with minimun space requirements, not just volume. They also go into pretty good detail about parameters, campatibility, and care requirements.