For HN's audience, no, that's not hard. But this product is clearly not only for us, and you've also cherry-picked a very simple example.
There's also the aspect of downloading the page in the first place and dealing with things like authentication and bot detection which a product like this helps solve.
I personally don't have a use for this product right now, but I won't be so bold as to say I'll never find a case where using it wouldn't be easier or more cost-effective than hacking up my own solution.
