i ve never read or heard about the hardness of the sponge used by pro cpen players using 802
There are some articles by Rowden Fullen and Lars Borg, Sweden-based coaches; but it is true there is not much on it. Still, in China it is rare for pro and other serious players not to glue their preferred kind of sponge to their pips. Friendship 802 comes, in China, with a standard fast and hard white sponge which is ok for hard hitting and blocking, but Ding Song (the world-champion defender) used Friendship Magic Red Sponge (1.5) with his 802 top-sheet and many female players used 802 with very soft japanese sponges (30 to 35 degrees) to attack or to defend with. A modern version of 802 has the relatively soft Mystery sponge. The soft sponges are used for better spin potential, which is either needed for good chopping, or for bringing the ball down when hitting hard. It is, on pro level, also a way to make sure you are not at the mercy of your opponent's heavy spin - a hard top-sheet like 802's tends to reverse heavy spin a bit if combined with a hard sponge, which makes returns too predictable.
Europese short pips rubbers tend to have softer top-sheets and softer sponges as well, so their spin-potential is relatively high. To compensate for this (an SP shouldn't really be like an inverted) pips are often also longer and/or further apart than is the case with classic chinese pips.
There seems to be a trend in making new MPs which play like SPs, having greater spin-potential and better speed but also some sink-effect; Friendship Legend 105, for instance. Another trend is making SPs faster and grippier, like Palio's Flying Dragon and Power Dragon Biotechs, or the among female pro's very popular Haifu short pips.
But it all comes down to the same: you need some grip if you want to be able to manipulate the ball well. A soft sponge is one of the ways to get it.