I concur. Upon further analysis, it appears that a rigid sleeve would possibly cause the filter threads to be sheared off in the event of contact with really hard things, like Jaywalker Noggins. I can see this thing in my head, a 3/16" sheared and cross-stamped chrome moly steel skidplate held on with six grade 8 bolts.

2005 Model . Two Fast Eddy stickers , a bell and a clock . She's Lola . She tinkles and keeps time . http://s649.photobucket.com/albums/uu211/britbike05/