I don't often use the expression "talk is cheap", probably because I like to talk and also because I believe words matter in many circumstances. However, I have to agree that the common expression "I'll try" is a prime example of when talk really is cheap.
An old friend of mine taught me about what linguists call a "word-to-world" fit. Part of what that means includes keeping the promises you make to others, even if you don't think you're making a promise. When someone says "I'll try" to me, I hear that person making a promise they will sincerely attempt to do something. But my experience with people who regularly say "I'll try" is, more often than not, nothing comes of it. I do not have the expectation people will always deliver on what they say they will "try" to do. But I do expect to know at least what became of the attempt. In other words, some follow through, at minimum. Even better for me would be if the person simply told me up front "No, I can't/won't/don't have the time to do that". Those statements at least have integrity.
I have a few other examples of when talk really is cheap to me but I'd rather hear yours. Please share some with me.