It's not that one totally ignores all things, some things for sure, but it's that they're not done to the same level of detail.
An easy test is give two different brewers one recipe (say Denny Conns Wrye Smile IPA).
Too much emphasis is given to ingredients, and not enough is given to process.
My club has done a couple of activities where a recipe was decided on, and ingredients were purchased and then split in to "kits". So everyone got the same malts and hops weighed out, and used the same yeast. Variables were water, equipment and process. The results were judged using a panel and BJCP score sheets.
The results were from the low 20s to the low 40s. Roughly a 20 point spread, I don't remember the exact numbers.
If anyone wants to try this it is a fun activity, and a learning experience for club members.