A few observations, the difference between platform up and platform down is the same on the compact models, 13". On the larger models, the difference is 15".
The 36" deck is a bulkier deck for its size because the 2 blade design, v.s. the 3 blade design, that is probably why the difference in length. The walk-behind mowers are the same way, the 36" is longer than the 48 or 52" mowers.
I assume the ' instead of " would be a typo. I am amazed how often there are typos in manufacturer spec sheets.
I don't know about the gallons, but considering how fast I use the gas on my Grandstand with a 23 hp engine, I would be glad to see a larger tank on it.
I see that they do need to update the link on the right side of the page.