In general, they ought to be similar, at least up to a point. People that invest this way are all investing approximately the same kinds of deals. However, Romney, like any principal in a partnership, stood to do better in a couple ways in all probability:
- Bain likely got significant fees for doing the various buyout deals. 20% of the total deal value is not uncommon. As a partner, he'd have gotten a piece of that fee.
- Using various (legal) mechanisms, Romney's end from these deals would be treated as "compensation" and probably more of it would be able to be tax deferred than the other investors' for whom the money was a profit on an investment and thereby taxed immediately.
- As a partner/employee at Bain, he probably had access to deals that their smaller investors would not. That is, he could get into syndicates that others would not be able to .
None of this is remarkable or unethical so long as no fraud was involved.