I mentioned this on another thread.
I think the key difference when it comes to the solo album versus the Smashing Pumpkins is the intention behind the writing. In the course of a number of interviews I've done with people that have multiple music projects, most musicians are able to separate the material that they use for each band.
One direct example. I interviewed Ted Stevens of Cursive, who also plays in Mayday, and asked him about the writing process for each band, and how he knew when he wrote a song whether it was a Cursive tune or a Mayday tune. And he said it was pretty clear from the outset where the song was going to end up. It had to do with mood and the initial songwriting goals.
I imagine this is the same for most musicians. As a musician myself, I know when I sit down to write something for my band, its different than when I sit down to write something for myself.
So when it comes to the Smashing Pumpkins, I think the name is indicative of Corgan's intent. Zwan set out to be a different project (read this interview I did with Jimmy Chamberlin to see his take on that:
http://kyndmusic.com/june05/chamberlin.htm) in terms of artistic intent, and ended up morphing into something else due to label pressure.
Corgan's solo record is the same thing - way more keyboards, different collaborators, and ultimately a different product.
I think the Smashing Pumpkins name is reflective of Corgan's songwriting intent. And I think the first single definitely supports that - "Tarantula" just DOES NOT sound like Zwan or TheFutureEmbrace. It sounds much more akin to the Smashing Pumpkins than anything else Corgan has done.
Prolific songwriters are like that. Look at Ryan Adams - he has all kinds of random stuff that he does that ends up under different monikers - The Finger, for example, or doing a record "& The Cardinals" versus just using his name. They're just labels that represent the intention behind them.