a couple thoughts
talent is simply the innate capacity for an individual to achieve x. As it is innate it is therefore genetically determined.
it is patently false to claim that all people have the same measure of talent; ie the same genetic makeup.
but it is absurd to claim that talent -- genetics -- should govern the amount of effort one expends to acheive a goal. If you don't see improvement going to 80 from 50, then go to 100. Then 110. Don't blame lack of 'talent' for 'success'; for both success and talent are ultimately relative. What's not relative is how hard one works to realize his potential.
talent, ie innate capacity, exists on a continuum: individuals have varying degrees of capacity to acheive a goal, whether a 2:10, or 2:30 or 3:30 marathon. Not everyone can run a 2:10 - for some it is in fact genetically impossible. There is no threshold at which one is considered talented. I have a 2:34 pr. I one who has a 3:34 says that I am talented, then I can claim that a 2:14 guy is talented as well.
but this does not absolve me of the responsibility of maximising the effort to acheive the best I am capable of.
person A is faster than person B. Person A say person B needs to run more, which is true. Person B say person A has more talent, which may also be true. But it's doesn't mean person B shouldn't run more and train harder, longer and faster.
Reminds me of the george carlin quotation in which everyone who drives slower than you is an asshole while everyone who drives faster is a maniac. Talent is like that: relative. Effort is absolute: work your hardest and you can be satisfied with the outcome.