So, no. Don't make you framework decision based on what your platform provider has to offer. Do it the other way. Make a decision on your framework, then choose a provider.
If the question is provider vs. own hosting? There is nothing wrong with using a paas-provider for a startup. Make sure there is no lock-in.
Blobstore really only exists to work around the lack of file access in AppEngine.
The pricing is something of an advantage, but don't choose it on that alone. If you know Java (or Python) already then it's worth using, but it's probably not going to give you enough of an advantage to switch platform.
I do Java AppEngine work in my day job, so if you have questions let me know.
(When you say "enterprise focused" do you mean your application is enterprise focused, or do you mean GAE/J is? Because there are some issues with using GAE for enterprise software and it's important you have considered them)
The main problems are as follows: 1) Data privacy. Usually this is just people worrying unnecessarily, but sometimes there are legal requirements about where customer data is stored. These may be jurisdictional or geographic requirements.
2) Integration issues. Enterprise software is all about integration. The AppEngine integration story is getting better, but you'll need to understand the SAML based single-sign-on support that is built into Google Accounts and/or implement it yourself, and you'll need to become familiar with Secure Data Connector (http://code.google.com/securedataconnector/) to integrate with private data sources.