That's because Uncle Iroh's first voice actor was named "Mako". Sadly, he died during season two, and then Greg Baldwin started voicing after him, hence the memorial message in the episode you mentioned. The character Mako has the voice actor's name as a tribute.
I winced a bit when I heard Dante Basco's voice coming out of this guy, thought it was a little to obvious homage. But in the last couple episodes when he was all "Oops, lost a sleeve because I'm bringing out the gun show...no seriously, shooting down planes over here", they won me back.
Sad face D: Although his voice is Zuko's, Iroh II looked too ... well... "aged" per-say for that voice to fit. We're all used to seeing this voice attached to the face of a ... well... I'm guessing he was 14? At the most 16 at the end of the series? !6 year old!! Its just.... well... misguiding ;__;
Well I'm just hoping they dub the series in my country because I watched ATLA like that, and I couldn't watch it with the original voices anymore. To me they sound like some typical prissy American teens. XD No offense. But yeah I watched the clip and his voice indeed sounds a bit weird. If we did the same and put Zuko's VA to do his voice....I don't think it would sound that bad...his voice was a bit more...flexible I think.
Funny thing is that Mai's voice was quite good in my opinion lol. I had the whole collection on DVD and I showed it to my friend; then I showed original clips to her and she was like; "Uhh....Katara sounds like some cheerleader...Zuko's voice is less emotional...and god Sokka sounds like he is ONLY comic relief, he sounds like he's stupid. And Toph sounds annoying. I don't like this, their voices are like from some show about rich american kids who party on a beach and so on. " Especially after that I cannot take the voices seriously, lol. XD
But yeah I quess they just wanted to make sure that "oh yeah this character is totally related to Zuko, get it??" But they could have showed it some other way I think. XD
I totally ship korra x Iroh after seeing this beautiful, handsome, firenation man. Forget Mako, I never liked him and Korra! I'm a Borra fan, and now a...korroh? Irroa?..... WHATEVER THE NAME I'M NOW A KORRA X IROH FAN!!!!!