This is the case in most jurisdictions but the line between expenses that are incurred in the course of earning your income and those which are not will vary to some extent.

For example, the cost of driving to and from work is generally not deductable, but if you need to travel to some third location then that is generally deductable.

It doesn't really matter exactly where the line between deductable and non-deductable is, because the same rules are applied to everyone in the jurisdiction. For example, if you decide that everyone can claim the cost of driving to work, then the tax rates need to be higher to ensure sufficient tax revenue for the government.

That said, you're correct that the difference between a corporation and a person is the extent to which their activities are income producing. Everything a company does is in the pursuit of profit, so all expenses are deductable against income. In fact tax law prohibits company's spending money for other purposes.