It doesn't fill the same role because it doesn't net you a card. 2-for 1 with a ~30-40% chance of whiffing is a night and day difference from scry 2. Scry 2 will only incidentally get you virtual card advantage if you're desperately digging for something, badly need a land, need to put lands back on top, etc.
These are extremely unlikely scenarios on turn 2, to the point that I'd be comfortable saying "scry 2" is worth a card less than 20% of the time.
So we have a 60-70% chance of getting a real card vs a sub-20% chance of some virtual card advantage that's otherwise selection.
The scenarios where you lose desperately needed lands or creatures to augur are irrelevant. It's just as likely to put unnecessary lands on the bottom, getting you to required spells -- putting three cards from the top of a randomized deck on the bottom is not a downside at all. If you hadn't known what cards went on the bottom, you'd be perfectly comfortable with that outcome.
Remember: Magic is a game of chance, so probability is more important than potential results. With a results-oriented mindset, Augur can whiff and put necessary cards on the bottom, so Omenreader seems like a good choice.
Thinking statistically, Omenreader isn't even a comparable card (except in that it's a 1/3).
W/U control doesn't exactly have 'dead cards', except Supreme Verdict in mirrors -- where omenreader's body is utterly irrelevant anyway -- and lands when you're flooded, etc. Scenarios where you'd be moving a dead card from the top to the bottom will happen so seldomly on turn 2 that it's hard to consider Scry 2 to be worth a card even a fourth as often as Augur's ability.
onder doesn't work because Index is simply rearranging w/o a draw. Scry at least gives you the option to weed out things you don't want.
