OK, so what evidence do you have that Dell doesn't mark that as $150 for software and $29 for installation, on their accounting system?
1) There is no evidence that they internally account for software as you say. It's speculation.
2) There IS evidence that they are charging for free software.
3) There IS evidence that they actually give a discount for installing software versus buying it from them separately: You can actually buy Office Home and Business directly from Dell for 219 USD. So they're actually giving a discount when they install it, as they only charge 179 USD in that scenario.
What does the evidence show? Seems clear to me.