For e.g. Bristol to Southampton, there's no ticket acceptance via Reading. Can't recall if there was when the line was closed for some time by last month's collision. If there was, and isn't now, that's inconsistent.
Mark
I suspect the difference is between disruption - unplanned, and tickets may have been bought for a route now impossible - and engineering - tickets were bought knowing (in theory) the possible options. And going via Reading is always an option.
But that journey is odd, for tickets and pricing, in any case. The option via Reading (called "not via London") is nearly twice the price of the route via Salisbury (for the SVR it's £85.40 vs £37.10, though there is an SSR at £63.60). Why the higher fare? It's not as if it's quicker - quite the opposite. At the moment there are advances available via Salisbury (afternoon) but not Reading, making the difference even greater.
SWR» 's advance information points out that the route is run by
GWR▸ and refers you to them. GWR don't list any block at Salisbury in their advance information. For some shorter journeys GWR do say you'll be on a bus from Salisbury - but they say's it's replacing an SWR service! That may be true if the journey (like most during the day) does end up on SWR services, but even so the lack of alignment looks bad. Incidentally, the advance notice PDFs don't align in any case - GWR's as for Sat-Fri and SWR's for Mon-Sun.