It seems like
max_price aren't generally accurate in
catalog_product_index_price for simple products using tiered pricing.
I haven't yet drilled into
Mage_Catalog_Model_Resource_Product_Indexer_Price_Default to get a better idea of what's going on under the hood, but I've taken a look at the sample data.
Here's a product using tiered pricing:
And the values in
catalog_product_index_price for it:
I would think this would be a perfect place for
min_price to reflect, well, the minimum possible price for the product. It does seem that the
tier_price column perhaps contains that value though.