What is 'normal' temperature anyway? Every day the weather forecasters posst the day's high, low and normal high and low temperatures, while some post the days high, low and average high and low temperatures.
I think in that context, "normal" and average" are interchangeable. But I could be wrong.
How do they know what's normal or average? Recorded temperatures have been around only 150 years or so.
That being the case, they know what's normal or average for the last 150 years or so. It's all they've got .

Soil samples and ice core samples will yield clues only so far back in history. The earth was probably really, really hot when it was forming. Does this in any way figure into the formula?
Something tells me that when your local weather folks are figuring average temps for the area they are not taking the formation of this planet into account. Call it a hunch.

And ice core readings are pretty useless for figuring temps in a small area, especially when that area is thousands of miles from where the samples were taken.
Do they throw out abnormal highs and lows? Shouldn't they in order to reach a more accurate mean average?
That's a good question, and it may lead to an answer to your first:
Maybe "normal" means the average minus "spikes" and "average" means an average derived from all readings...
