Today, I was reading up on different types of loans - specifically, a fully amortizing vs. partially amortizing loan. I encountered the following table illustration:

What I notice is that with amortizing period loan of 20yrs at 10yrs loan term vs a fully amortized loan, even though the partial amortizing loan monthly payment is 27% less, the total dollars paid out to it is only 19% more! I would have assumed that if I paid 27% less per month, then I would pay 27% more in the end. However, what this table is showing is that I can pay 27% less each month and only have to pay 19% more in the end, saving me a difference of at least 8%. This isn't even taking into account the higher interest deductions. So am I interpreting this table correctly - that I should always try to go for a longer amortizing period assuming the same loan term? Is there something I'm not catching?