Fragmenting tables/indexes

Hi. We have a system that we have fragmented based on Date so that when we purge our system on a daily basis we simply drop the oldest fragment. This part works superbly, but retrieval of records seems to be unneccesarily slow. I believe that what we need is a separate dbspace for the indexes, but other DBAs feel that this will cause more problems because the indexes will have to be rebuilt to drop the data fragment. Am I wrong to assume that the index pages will work like data pages and simply "mark" the rows that are no longer used, and reuse these spaces as needed for the next day's data? FYI the table has more than one index, and only one is organized with the date field first.