no, it does not, you jus keep different templates, for yahoo finance it maybe extra 100 files. I worked for the small company and we managed it. Basically, you have 1 web site, you just define via "user-agent" a type of device requesting the web site and present the website in the corresponding template. No extra expenses at all. The problem with big companies like Yahoo is that there are huge number of middle men between developers, customer support and decision making management. Many often these middle men have no clue what is going on and "their main job is to keep the job" - show his/her position's importance. As the result, the decision making management has no idea about customers needs nor they have clue about developers recomendations.
Why not? The original Yahoo Finance page was very good for option and stock quotes, the new site sucks. Check Yahoo Finance for stocks, option chains and quotes. Decide on trade. Log-in to broker account for final quotes and open trade. Track the trade with Yahoo Finance. Log-in to broker account to close the trade. I'm sure lots of pros use Yahoo Finance.
Considering how different the old and new websites are, I feel like you are trivializing the amount of work involved in such an operation.