What? Is that true?
No. Most modern game engines use time based animation rather than frame based. So a variable frame rate is not a huge issue. For example, if the raw animation data is keyed at 30 fps, with keys on each frame, the time step would be 33 ms between two keys/transforms. Rather than update the transform at the start of each frame with raw keyframe data, you update with interpolated data between two keys, while keeping track of how much time has passed.