To be honest I think the whole Uruk-Hai attack plan needed re thinking, commiting to a large scale assault seems to be a flawed plan alltogether, the Uruk-Hai would of been able to plan a full scale siege and been able to succeed in this very easily due to their pure numbers and the speed at which they were being made any losses they encountered due to food shortage would of been negated by the fact that they would still probably of been gaining orcs rather than losing them and the orcs they did lose would of been able to of been used as a food source in themselves the humans however would lack the stanima and lack or morales that the orcs held in their favour, they would of been unable to gain troops due to the position of Helms deep and so would of been starved out quite rapidly if you look closely their food storages would of been un sustainable for a decent length of time and so they would of been starved out quite quickly.
Also the orcs proved in the movie and book that they were extremly efficient workers and were able to dig out massive areas of land, so this follows that if they were able to manufacture bombs then they would be able to commit to siege warfare using the techniques used by civilisations far before bombs were created, digging siege tunnels below the walls and then collapsing them and that would render the defences virtually useless if repeated enough.
The Uruk-Hai would of been able to set up an effective rear guard with pikes barricades and arrows at the top of the ridge and down the valley that the Rohirrim came from and due to their lack of foot soldiers would of been able to hold them off long enough for them to capture the stronghold.
I think in my opinion that the Uruk-Hais downfall would of more been their lack of leadership and strategy i mean saruman was basically a traitor and Sauron was a massive eye/spirit unable to engage in the most simple forms of comunication this is reflected in the almost fall of Minas Tirith where the stupidity of the steward Denethor,Both sides had the resources to with stand an attack or siege and both sides suffered massive loses when led by idiots i suppose it all comes down to not what you have but how you use it.