John,
...Lr history is more like a record of transactions which may not be an oddity in general database-driven apps but is certainly so in this class of software. Unless you can cite another raw converter or photo cataloging app that offers it...
If I understand Paul correctly, Capture NX2 is another RAW converter that lists adjustments made by the photographer as a series of steps.
Like Paul, I too enjoy having a list that indicates adjustments in the order in which they have been made, which may be re-edited, moved within the 'stack', toggled on/off or deleted if need be, at any time. An undo button, by comparison, strikes me as a crude alternative solution, as it does not allow the photographer to see the effect of a change made to an earlier adjustment
within the context of the effect of later adjustments. At least, not without having to reapply the subsequent steps again, which presumably requires the photographer to remember or note down the relevant value adopted for them.
Cheers,