Burning 25GB discs is only useful if you absolutely cannot split a >4.3GB file into archives.
...Or if you have a hundreds GB of data and would rather use 4 discs to back it up rather than 25. Not everyones needs are the same...
That said, Blank Bluray discs are definitely still cost-prohibitive. the cheapest I can find at newegg.com is $7.99
per disc, but namebrands like Sony are $19.99 for a 25GB disc or $37.99 for a single 50GB dual layer disc.
At the same time you can buy a spindle of 100 DVD-R's between $20 and $30, depending on the brand.
Given those prices, and that BluRay's market share is still fairly insignificant compared with 'normal' DVD's (both in movies and other applications), I doubt that plain vanilla DVD will be going away anytime soon.