TCP only gives you 16 bits of checksum, which is really not enough. I used to work for a CDN which served downloads over HTTP, and when the object size grew to a few gigabytes a non-negligible percentage of users ended up with corruption.
The SSL MAC is valuable even in the absence of enemy action.
If you want to buy real estate in small liquid increments, you can do that with REITs (essentially real estate trusts that trade like stocks).
I live in an apartment owned by one of the big publicly traded trusts, and have amused myself in the past by calculating how many shares I'd have to buy for the dividends to cover my rent. On balance there are other ways I'd rather invest my money though.
The SSL MAC is valuable even in the absence of enemy action.