Technically as soon as a 100-beatmap megapack was released, the minipacks were implicitly obsolete. I'm planning to make this situation more explicit, as once a 100-pack comes out there is really no need for the leading 10packs.
10packs will still be registered on the tracker (unlike the currently announced deprecated ones which will be removed) however they will not be listed on the osu!torrents page, and will not be seeded on my 'official' boxes. Others are welcome to seed, but everyone would be better off if the megapacks were seeded instead!
For anyone concerned about bandwidth use on the megapacks (i.e. downloading too much at once) they should be reminded you can select which files in a torrent you wish to download (standard functionality in most clients) and most clients also support download quotas to prevent going over any limits.
Edit: I realise I should probably clarify between obsolete and deprecated here.
Deprecated torrents are ones which will be removed from the tracker as they have been completely succeeded by another. In this case an entry and note will appear on the listings. (Example of this would be 401-425/450 451-500, which would be replaced by the full megapack)
Obsolete torrents are ones which still hold some meaning and will not be removed from the tracker, but should not be used as new (such as minipacks leading to a megapack) for the full set, only to update an existing collection (like for seed boxes) and will be removed from the 'official' boxes after a while.
There will be more information on the pages soon detailing anything I can think of, though I'm trying to balance time between documenting things, or improving the backend to provide more info~