I think Rob did a find job on the chart and you can learn a lot from it. It's a godsend if you're building an AR or buying a complete rifle. Maintaining the chart must be a nightmare but he keeps it up to date.
You can deviate from the left of the chart where the Colt, LMT and BCM are yet still end up with a fine AR. If you believe a 1:9 twist is better suited to the ammo you'll use, go ahead. If you ended up with a commercial receiver extension but aren't changing the slider, no big deal. If you don't have the F-marked FSB, it can be corrected with a taller sight blade. Go ahead and buy a midlength gas system even though it's not milspec.
The things that are most important are the bolt/carrier and barrel. Make sure yours are robust and reliable.
Don't get angry at the chart, learn from it and avoid mistakes. If you do deviate from it - know what you're doing.