First, let me agree with Ripley (saves me having to type duplicate text).
As was discussed way back when, the Sherman project was an elegant solution to deliver multiple kits quickly and accurately. The Sherman I, III and IV use common components extensively. The Sherman II has a more complicated hull (lots of odd curves) plus Rubicon decided to supply a new set of running gear. There is plenty of discussion on that on the Sherman project thread.
When the Sherman project started, a number of us asked about the Sherman V. Rubicon said that they were aware that a plastic version was in the pipeline from someone else, and because it was effectively a different vehicle (it would share turrets at the sprue level) it would not be a priority.
That they have designed and are progressing the Sherman V is great.
There may be some issues with their initial add on packs, which from your posting and other comments indicates that base vehicle and add on packs are being bundled. That is to be expected over time, and might indicate an evolution in marketing approach based on feedback. Another example is the 251 multi-kit, that probably contains lots of nice stuff that most wargamers do not need, when they are after a base half track. Hence that evolved into the add on kits.
The Sherman and Panzer IV are bread and butter tanks, Rubicon's clever engineering and design has allowed them to supply a large range of variants and that will appeal to the wargaming modeller.
Their more off-the-wall models (fencing, walls etc) are as Ripley pointed out making money from test piece development.
The giant mortar is one of those "look what we can do" centre-pieces, they will not sell many (possibly - though if you look through the Forge World catalogue, I may be wrong).
