There is no penalty for non-filing if no tax is owed. So in your example situation, while the IRS dictates that they are obligated to file (assuming their income exceeds the minimum threshold) and their withholding was sufficient, there is no penalty for failing to do so, the IRS is happy to keep unclaimed refunds.
Unless you go through the return, you cannot be 100% certain that you will not owe, employers mess up withholding, employees put an incorrect number of allowances on their W-4, people have other income, etc. I'd argue that requiring a return gives them a more defensible position when coming after someone for non-payment, and discourages people from taking the risk of not-filing.
I'd imagine filing in most years and skipping some makes you a prime target for audit, but as I said, they're happy to keep unclaimed refund money.
Edit - Clarification and some sources:
The failure to file penalty is the lesser of 100% of tax owed and $205, so if your withholding was sufficient (no tax owed) then there'd be no penalty.
When you fail to file a return and should have, the IRS, in essence, does it for you using an SFR (Substitute for Return). This basically assumes the worst based on evidence they have, i.e. you sold stock, they assume $0 basis since they lack any other information, you had 1099 income, they assume no expenses offsetting it, etc. For most simple returns the SFR is identical to the return that would have been filed, so this triggers no adverse action since they will discover no additional tax owed.
This is at the IRS level, and for personal tax returns, partnerships/S-Corps, etc face different rules. State laws may vary.