There are some such features, such as interfaces to heart monitors and cadence sensors. The question is then whether those features are important to you. I've been using GPS units in lieu of bike cyclometers for over 12 years and none of them were marketed as cycling-specific. My Garmin eMap was bought in '99 and is still my most used GPS for cycling. It's been discontinued but can be found for under $100 and provides speed (current, avg., max.), distance, elevation, detailed road/topo maps, points-of-interest (esp. handy on tours for finding food, lodging, bike shops, etc.), and keeps a detailed tracklog so I can download trip details to my PC to compile data on speeds, elevation gains, and performance comparisons between trips. The tracklog also lets me record where photos were taken and create trip records like:
http://www.everytrail.com/fullscreen.php?trip_id=502372
from yesterday. Personally I have no need for the cycling-specific models, but YMMV.

For that matter I also use the same eMap for boating, hiking, and general travel in addition to cycling. Other GPS units that I've found well suited to cycling include the Quest and GPS V - both of these do automatic routing (you can set preferences for cycling/ped/car so you don't get routed on roads that don't permit cycling) which the eMap does not. All of these have long battery life which is one feature that's lacking in many car-oriented models.