Personally, I prefer the painting board because it helps me focus on a single project at a time. The closest I came to a panting blog style thread was my Harlequins. Also, if people are looking for inspiration on paint schemes and how to do some things, it helps to focus their search.
Using my recent work on Guilliman as an example. If someone is looking for ideas on how to paint the model and they see a thread titled "Triumvirate of the Primarch," then they know they are going to see three possibilities in there - Guilliman, Cypher, or Voldus. On the flip side, 10 pages of "Killersquid's projects" may be daunting to go into, and you really have no idea what you will find in there.
There is also the angle that by pulling up a thread in the Painting Board, I know what I am getting. I am either going to see the various stages of painting, from beginning to end. For someone like me who has very little interest in massive conversion work, I don't particularly care to look at progression pictures of someone making a plasticard Stompa.
For me, the Painting Board will always be relevant. Some people prefer to group all of their work in a single thread, others do not. I am the latter and will keep flooding the board with new threads for new projects! Besides, there may come a day when the front page is just covered in my threads, and I am narcissistic enough to be ok with that lol