You can still power mons to 40 with multiple devices.
Answers
The difference is that email accounts are free and you can make as many pogo accounts as you want with no breadcrumbs for niantic to trace; given the anonymity of email accounts (*could maybe trace via IP, but that's another topic). However, logging into different devices at the same time flags their servers (you get locked out, cant spin stops, or catch, etc), so it's very obvious abuse of the TOS. What's worse is that if you do this "trick" to push a pokemon to l40 then you will have that evidence of the violation on your acct forever (or until transfer of said pokemon.)
The fact remains, that all niantic would have to do is a simple SQL query to expose every account with level 40 pokemon. Like I said, use at your own risk.
I get wanting to power up all your favorite/high IV pokemon to max level (40), trust me, I get it. I'm right there with you. I just don't see the risk/reward make enough sense to do it.
Wow, a player who has 1+ million dust is a botter? How dumb are you? Don't be envy of people and don't do false accusations on other people. If you don't have 1+ million, there are only 3 reasons.
1) You are just plain lazy and doesn't walk around catching Pokemons everyday.
2) You are a spoofer yourself who spoofs just to catch a single high IV Pokemon everyday, hence you don't have enough dusts to power up that very high IV Pokemon.
3) You blindly powered up most of your Pokemons without checking their stats, IVs, CPs and their offensive/defensive output in gyms and raids without doing research.