1. Web reporting is faster then Excel, there is less overhead in executing Web reporting as opposed to Excel. (Whitepaper on SAP about this.)
2. There is not anymore work in formatting or creation of templates then in comparison to workbooks. 
3. Query creation is the same as in BEX, so there is no new knowledge there.
4. Yes, knowledge of HTML is needed, but if you use the standard CSS templates, you really don't need to know them unless you want to change them. But, if you can write queries or code ABAP, you can definitely learn basic HTML and CSS to customize reporting. Its not that hard. 
5. The learning curve for NEW users in Web Reporting vs.. BEX is actually considerably lower. Most people are very familiar with using a web browser, and IMOE I have found they pick up usage of web reporting much quicker then trying to teach them BEX. 
6. Note, if you have a large user base which is already power Excel/BEx users, then they might be more reluctant to switch, though they would have no problem learning quickly the web reporting. Their downside would be that the behavior is not like Excel, which is a learned behavior, though the functionality is the same.
7. Publishing of queries and reports is done (or can be) via a role template which can be published on the web to provide common access to reports and queries.
8. Your implementation team (or at least one person on there) could be designated to picking up learning creation of web templates. (Its not hard, really.) Depending on organization size you may not need an additional person.
9. Publishing can be as easy a link on an existing intranet, or if you are using Portals already, integration with Portals is straightforward and you should have the knowledge base for doing so w/ your Portals group.
10. Query functionality is EXACTLY THE SAME with BEX and Web reporting, they both use query analyzer. The only difference is in presentation and output.
11. With Web reporting, you have (I think) greater control over presentation (combination of reports, charts, etc...) then w/ BEX.
12. You can provide the ability for "Printer friendly" versions of web reports, you can also provide the ability to easily pull the results into Excel in standard format or CSV format.
13. Finally, I think you have the ability to open up reporting and information consumption to a wider audience then in sticking w/ just BEx. (It definitely has its place in the organization.)

Also read

• Questions Answers For SAP Business Warehouse #1
• Questions Answers For SAP Business Warehouse #2
• Questions Answers For SAP Business Warehouse #3

SAP Business Warehouse Books
SAP BW Books - Certification, Interview Questions and Configuration

Best regards,
SAP Basis, ABAP Programming and Other IMG Stuff
http://www.erpgreat.com