So.... why didnt Roth just send someone in and take it?

He obviously knew when it wasnt there and then knew when it was... he could have whacked Michael earlier and taken the money too...

What was he waiting for? For Michael to actually personally hand it over to him? Was he that "into" the whole chess match thing?

Did you see that mean looking body guard who was keeping an eye on Michael and his money? Are you kidding me?

It could also have been pride on Roths part, that he was more powerful then mike and wanted mike to give him the money personally to show he was the top dog.

Short answer: Filmic device. Of course Roth could have had Michael (and the bodyguard--formidable as he looked, he was only one man) whacked the moment he stepped off the plane in Cuba. Or he could have had his pals in the Cuban government arrange to grab the money (at Customs) as soon as Fredo stepped off the plane. But that would have deprived us of the supremely satisfying cat-and-mouse game he and Michael played out, to our everlasting pleasure.
Longer answer: Roth needed to have Michael hand over the money to provide him with an alibi and longer-term insurance once Michael was whacked. As I said in another thread: the birthday party scene was designed to provide Roth with an alibi in case Michael's successors started asking questions once he turned up dead (or was missing): "Hey, I loved the kid like my own son. I was gonna turn over everything to him. Just ask those fat thugs who were at my birthday party..."
Also, simply overwhelming Michael and/or having his money confiscated would be equally damning for Roth. I believe he intended for Batista's secret police (SIM) to attack the military car that was going to take Michael back to his hotel after the party, and kill everyone inside the car--making it look like the rebels did it, not knowing that a gringo was in the car with Batista's soldiers. Then Roth could have said, "Gosh, I'm really sorry about this...looks like poor Michael's a victim of the rebels."

He would have done that really melancholy tone he could summon and he would say, "On my birthday I told him not to worry about those rebels....how I wish I could take that back now that he is gone."

"I'd give back the two million to see him again, oh, and to be able to take a piss again without it hurting."

But it seemed Micheal was sure about his safety when he observed Roth's birthday and a while back when he approached Roth's house in America. A little strange? Don't you think

Michael seemed certain of two things: that Roth wouldn't move against him until he got the $2 million; and later, that Rth wouldn't try to whack him until after he left the Presidential palace. So he figured that if he struck first, he'd be ok. He also arranged for a private plane to take him out of Havana, which was a good move.

Ok... but Roth really had no bodyguard protection...(especially, alone in his bed when deadman walking goes to suffocate him)... he never thought that Mike would strike before leaving after New Years Eve party?

Maybe he underestimated Micheal too much. He might think Micheal had not figured out his true enemy and the whole thing was totally under his commands.

Yes! A subtheme running through the entire Trilogy is how people underestimate each other and suffer the consequences. Vito underestimated Sollozzo. Sollozzo underestimated Michael. Tom underestimated Carlo. Geary underestimated Michael. Roth and Michael underestimated each other several times, which adds to the complexity of their scenes together.