And history still shows that, even when heavy ordnance neutralizes hardened targets, some poor ground-pounder still has to go in and do heavy fighting. Buna-Gona is a great example: an entire National Guard division was sent into a swamp with one artillery piece in support, and fought their way through hell for months to gain yards at a time. When they finally got support commenserate with their unit and mission (some Aussie 25-lb guns and light tanks), they finally cracked the defenses around Buna...and fought their way through hell for another month.
Of course, Buna's an extreme example, since (with the possible exceptions of Milne Bay and New Georgia) it might very well be the most malignant terrain on the entire planet. But heavy support weapons - bunker-busting bombs, heavy artillery, etc. - usually doesn't make the bloody infantry's job any easier. Just quicker.
That's also something to keep in mind when you see and hear military and political leaders talk about making war "friendlier", or about fighting wars exclusively from the air (a la Bill Clinton). Never works. Never. War always sucks, because it always involves some poor schmuck wallowing in the mud while dying from a high-velocity gunshot wound.