The German, British and American armies could do that. It was part of their operational capability. They had the communications for it. They trained for it. The Russian army didn't have the radios, nor the training, nor the operational control at that level.
Please, let's see the citations from historic sources to back up a statement like that. Or is this just one of those things that 'everybody knows'?
Regarding the use of katyushas: they were most usually used prior to an assault as they were by no means a precise wepon simply due to their very nature.
Example - a rocket brigade firing M-31s (8 rails with 300mm rockets per truck) covered an area of 42 hectares (about 100 acres) with about 18 rockets landing per hectare. This means about 7-8 rockets landing in the area of a football field. They also had a
minimum range of 2,800 metres.*
Sometimes brigades using smaller rockets would try to concentrate their fire to a concentration of 20-30 rockets per hectare. It is also worth noting that a heavy rocket would usually destroy a light or medium vehicle or a gun if it landed withing 5-10 metres.**
So a barrage was certainly enough to mess up vehicles and gun emplacements in a large target area but not enough to inflict more than low to middle percentage casualties amongst dug-in troops. Their morale, however, would be through the floor shortly thereafter.
*Prokhorov, I & Trusov, V - "
Reaktivnaya artilleriya v Velikoi Otechestvennoi Voine," Voenno Istoricheskii Zhurnal, Moscow, Vol 1-66, p. 5
** 1995, Armstrong, R N - "Red Army Legacies", Schiffer Military History, Atglen, PA, p.23