It's true that it cannot be all things to all people. But if steemit is purporting to ascribe value to blogs/posts then it cannot say that what is valuable today (29th August), is not valuable on the 29th September. It should have some component of payment that pays after say, 6 months and perhaps even after 5 years. If it wants people to remain in steemit, this would fit in with the business model, as people would be loathe to leave, if they knew they had their forthcoming 6 monthly payment to come in a couple of months' time. It would fit in with the ethos of their company. Of course, I wouldn't want steemit to hold back massive percentages but a suitable percentage would be appropriate. It would also provide further stability to the company in the long term. It would also give a chance for 'failed' posts (where the poster had perhaps worked very hard, but posted at the wrong time etc) to subsequently become successful posts. So there are a number of reasons why they should do this, IMHO.
Of course, steemit is still in Beta stage so can address this issue.