According to 91.169, airplanes need 2,000-ft elevation while helicopters need 1,000 ft. Airplanes also need three set miles visibility while helicopters only need two. Is this because helicopters fly lower and slower than airplanes?
The reason/rationale for why helicopter alternate weather minimums are lower than airplane alternate weather minimums can be found in this Federal Register addressing 14 CFR 91.169 - IFR flight plan: Information required.
Here is a pertinent excerpt from the Federal Register (Titled: Flight Plan Requirements for Helicopter Operations Under Instrument Flight Rules), specifically "A Rule by the Federal Aviation Administration on 01/21/2000" (Final Rule):
(Below is an excerpt from the linked Federal Register paragraph shown above titled "Alternate Airport Weather Minima")
"The commenters stated that helicopter operators should not be subject to the same restrictions imposed on operators of other types of aircraft by the use of nonstandard alternate minimums. ... Due to the ability of helicopters to fly any available instrument approach, regardless of wind direction, and to land at the approach threshold regardless of runway length by pivoting into the wind, if necessary, just before touchdown, the commenters asserted that helicopter operators should not be restricted by these non-standard alternate minimums. They further stated that helicopter operators therefore should be allowed to use lower-than-standard alternate weather minima, regardless of whether standard or nonstandard alternate airport weather minima are specified on part 97 approach plates.
The FAA agrees with these comments. ..."
(emphasis is mine)