Revenue - Cost of Good Sold (Inventory) = Gross Margins (AMD wins here)
Gross Margins - Selling, General Administrative & R&D Expenses = EBIT (Earnings Before Interest and Taxes)
EBIT or also called "operating income" is a measure of a firm's profitability.
Remember how NV has 3 lines: Quadro, GPU, GPGPU? Well its R&D is subtracted from aggregate Gross Margins of all 3 product lines, not just discrete GPUs. Also, same for SG&A. So 1 firm has 3 revenue product streams with each generating cash flows, and economies of scale of sharing marketing teams, key engineers, etc. (although their GPU division on a standalone basis is probably negative right now). Of course this example is still too simplistic since NV also has minor revenue from Tegra.
Here is a simplistic way of thinking about it.
Say it costs $3B to design a new GPU. NV spends $4B to design a chip that will sell in all 3 product lines. AMD spends $3B for really 12% of professional market and discrete GPUs. Over the next several years, it will take a long time before profits from their 1 discrete GPU line cover their R&D spend. Since right now their desktop market share is around 51%(AMD) /49% (NV), that means NV has 2 more revenue streams to make serious $$$ despite relatively similar GPU architecture costs. Basically, the way NV has diversified its business into various product lines is a much more effective business strategy (you minimize your cash flow risk in case 1 of your revenue streams has a bad year). While if ATI flops a couple GPU generations, they would be in serious trouble. Maybe that's why their engineers work extra hard? 🙂