80pt does not really mean anything in Video. It means something for print since it is specifying the absolute size of the type. In Video one does not know the display resolution in pixels to properly translate points to pixels. a point being approx 1/72 inch.
In Vegas if you enter 80pt in Titles and Text and 80pt in Legacy Text you will get a different absolute text size. The reason being each is using a different approximation for the screen resolution. Protype titler does not try to bother with point sizes for text and just uses a 0..10.0 scale.
Most every app and/or titler is going to give something slightly different for 80pt. A better thing for someone to ask for is the text to be some percentage of screen height.
Likewise DPI being meaningless too, since it's an analogous concept. Consider also that if you really did produce 80pt on a phone screen, each character would fill about half the screen, whereas on an 80" screen it would be so small in pixels it might be illegible. As Norman says, percentage of screen height is the best measurement. If they can't answer that, you could produce a few sample still frame captures from the Vegas timeline with their text set in different sizes and ask them which looks like what they want.
Even in PhotoShop this size is relative, not absolute. If you change the pixels-per-inch setting your fonts will also change size. So, unless you know what PPI they were using in PhotoShop, what size document frame they're working with, what zoom level they have, and what size their monitor is, 80pt doesn't even tell you anything. It could be anywhere from microscopic to filling their screen.
I'm reminded of a conversation i had ages ago with an intern working on her first solo project, which consisted of a series of still images with animated text overlaid. She was asking what sizes to use for various elements. Every time she uttered "DPI" i immediately interrupted and said "DPI is meaningless in video", to which she would try to explain why it did apply in each particular circumstance. I'd merely shake my head at each explanation and say "no, it doesnt't." After about 15 of these she finally asked in exasperation "OK, i give up, i know i'm wrong. Please explain why." I got about 5 words into saying "you never know what size screen it will be viewed on" when she stopped me and said "Ooooooh! I get it!"
Really great information from everyone. I sent a copy of the thread to my client. He found it very interesting. Turns out that he arrived at his 80pt. request by laying out the screen in FCP. Don't know if he was in 720P or 1080. Anyway, he said he's going to stop obsessing about this stuff, which will make my life easier. In his defense, he oversees many more print projects than videos. So, thanks to all. What a group!