So using your same rhetorical style, let me respond:
- While the error rate of memory is "low" (however you define that to mean), it is not zero, so the risk of memory errors persists.
- A machine without ECC memory has no reliable way to detect memory errors without some type of external diagnostic.
- While a memory test can (hopefully) detect faulty memory, it takes the computer out of operation for however long the test is run, and even then, it's simply a point-in-time test. It cannot detect memory errors that happened in the past, or that will happen in the future once the test has ended.
- ECC provides a mechanism to reliable detect memory errors as they occur, continuously, while the machine is running and performing useful work.
- While many memory manufacturers offer lifetime warranties on their memory modules, they cannot possibly warrant against data corruption and malfunctions caused by memory errors, which can have a much higher cost to the user than the modules themselves (and would almost certainly be more than the BOM cost difference between ECC and non-ECC modules).
- ECC has been cited by Microsoft and Linus Torvalds as desirable and something that should be broadly adopted, and ECC is commonly found in a wide variety of memory products (e.g., caches and solid state storage), with the glaring exception of main memory on consumer PC hardware.
- While ECC does cost more (all else being equal), the side-band ECC being discussed is the same effective speed as non-ECC memory. The overhead of ECC is canceled out by the ECC DIMM's extra capacity and bandwidth relative to the non-ECC DIMM.
- While the error rate of memory is "low" (however you define that to mean), it is not zero, so the risk of memory errors persists.
- A machine without ECC memory has no reliable way to detect memory errors without some type of external diagnostic.
- While a memory test can (hopefully) detect faulty memory, it takes the computer out of operation for however long the test is run, and even then, it's simply a point-in-time test. It cannot detect memory errors that happened in the past, or that will happen in the future once the test has ended.
- ECC provides a mechanism to reliable detect memory errors as they occur, continuously, while the machine is running and performing useful work.
- While many memory manufacturers offer lifetime warranties on their memory modules, they cannot possibly warrant against data corruption and malfunctions caused by memory errors, which can have a much higher cost to the user than the modules themselves (and would almost certainly be more than the BOM cost difference between ECC and non-ECC modules).
- ECC has been cited by Microsoft and Linus Torvalds as desirable and something that should be broadly adopted, and ECC is commonly found in a wide variety of memory products (e.g., caches and solid state storage), with the glaring exception of main memory on consumer PC hardware.
- While ECC does cost more (all else being equal), the side-band ECC being discussed is the same effective speed as non-ECC memory. The overhead of ECC is canceled out by the ECC DIMM's extra capacity and bandwidth relative to the non-ECC DIMM.