Your misquoting the book
The discription says:
"Complete with tripod brace, silencer, and telescopic sight, in the right hands of a skilled marksman it can easily turnt he tide of a battle"
A standard SP sniper rife does not come with tripod and sight but when they are attached it makes a mean weapon. It does come with integral noise baffles which does the exact same thing as a silencer (if bulk is a hastle - house rule that it doesnt have the baffles and allow it to take a silencer at a later date).
In terms of the tripod/bipod situation, i see it more as a non-statable upgrade. sure some weapons like the rocket launcher can be braced on your sholder but things like the Hvy Bolter and Autocannon would need to be braced upon something (unless you have Buging Biceps) a stand alows the weapon to be off the ground and less ristricted by the object its braced on:
Impose penalties to rapidly changing directions of fire;
have the munitorium agent/ tech preists get angry at the damaged or dirty underside of the weapon;
have the Lascannon super heat the mud its resting on damaging the weapon / crew or miss the shot