Hmmm....apparently those studies (for enhanced immune and cardiac function) were all done in the East, and most were scientifically shaky.
Here's what Terumo wrote: "This falls into the additional antioxidant category. There are some tie-ins to EGCG and leptin, but those are somewhat unfounded. EGCG tie-ins to cAMP re-uptake show a bit more promise. If you want an extra antioxidant, choose vitamin C. After that, choose green tea, standardized for EGCG. A very strong POSSIBLY USEFUL"
I think that's why it's been such a successful supplement. Many green tea products I see out there today are enriched with Vitamin C, and they already have caffeine in them. So you're getting three excellent supplements in one: caffeine (for weight loss) and vitamin C and the EGCG (for antioxidant protection).