The author writes this:
"I don't charge less if I need the work and neither do I charge more if I am busy."
and then concludes with this in the final paragraph:
"Also at the end of the day, pricing is about supply and demand."
These statements cannot both be true - charging more because you are busy is the very definition of your work being in heavier demand.
Not about your demand - about the market's? You can be busy with 2 jobs overlapping, yet the market can be soft for lots of people and you underbid to get those jobs.
I get what you're saying but that's when we talk about averages and generalizations. It doesn't necessarily apply to an individual. For example, the average lawyer makes about 120k a year. A really good lawyer with a great local (and perhaps state-wide or country-wide) reputation will charge a lot more for their time since their time is a limited commodity. It doesn't matter that the average lawyer can still only charge ~120k per year. They can personally charge much more than that so the supply and demand aspect of the market a whole is meaningless to them specifically. Similarly, if this programmer/developer has a ton of skills and experience and can crank out code, they can conceivably charge a lot more for their time.
The way I read that is....as a general rule, set prices that are consistent and not based on your availability ...but if a client is desperate, and willing to pay you more to work over a weekend, then sure, make an exception to the rule.
These statements cannot both be true - charging more because you are busy is the very definition of your work being in heavier demand.